Metro leaders were told Thursday that long-term maintenance for the troubled second phase of the Silver Line rail extension will cost millions of dollars and necessitate the periodic shutdown of tracks — and possibly stations — because of construction flaws.

The office of Metro’s inspector general and the transit agency’s liaison to the Metropolitan Washington Airports Authority — which is managing construction of the project — told board members that progress had been made in correcting several construction flaws that have caused delays, but four outstanding issues remain. They said the earliest the six-station extension could open was July, but that the project will probably need a few additional months and should open in September.

Cracks in concrete panels at five of the six stations have been sealed with four coats of a sealant that will last about a decade, board members were told. Once the Silver Line is turned over to Metro to operate, resealing the panels will become the transit authority’s responsibility.

The panels, which were built to last 100 years, will need to be resealed every 5 to 7 years, according to the inspector general’s analysis. The cost? Up to $1.8 million every time, without adjusting for future inflation and lost revenue from having to take tracks off line for the work — and potentially stations too, because the panels are close to escalators. Metro will also need to pay for panel inspections every three months, and their results could prompt even more treatments with the expensive sealant.

But that’s only if Metro is comfortable with the solution, and it was apparent that Rene Febles, deputy inspector general for investigations and special projects, was not.

“Our concern is more with the panel than the application,” Febles said.

Febles and a structural consultant checked out all the panels and had them tested, with some showing high levels of chlorides, which could lead to corrosion. The sealant is supposed to protect the panels but Eldon Tipping, the structural consultant, told board members it’s not a perfect fix.

“I don’t think the product can be expected to be 100 percent effective in the locations where there are cracks,” he said.

Board members struggled with the financial cost of maintenance, an imperfect solution and public expectations to open Phase 2 of the $5.8-billion rail line by next year. The second phase of the project will provide Metro service to Dulles International Airport and Loudoun County.

Board member Thomas H. Graham said the issues sounded like a high level of deficiencies in the rail line.

“Is this the norm?” he asked.

Board member Christian Dorsey questioned whether the panels should have been replaced two years ago when the issues surfaced.

Metro, meanwhile, is moving forward, making plans to begin operations next year. General Manager Paul J. Wiedefeld has said the transit agency plans to privatize operations for the second phase of the line, and staff members said Thursday that board members can expect to hear cost projections in January, when they may be asked to include the amount in the budget. Wiedefeld said training for workers who will run the extension could start in six months.

The update on the Silver Line took place at a safety subcommittee meeting in a room next to the regular boardroom. Discussion and questions about the project caused the meeting of the full board to be delayed by more than 30 minutes. The board room meanwhile, was packed with striking workers from the Cinder Bed Road Metrobus garage and members of ATU Local 689, who came to confront Wiedefeld and board members. Nearly 130 bus garage workers have been on strike for 29 days in protest of the wages and benefits provided by Transdev, a multinational transportation company that Metro hired to run the garage. The workers say most Metrobus drivers hired directly by the transit agency have better pay, health insurance with lower deductibles and better retirement benefits. The Cinder Bed Road employees say they deserve the same because they do the same job.

For more than an hour union members took over the public comment portion of the meeting to lay into Metro leaders.

“You need to fix this problem now because you did this,” Metrobus operator Albert Ruffin said.

Throughout the meeting chants and cheers for speakers came from the crowd, many holding signs. As speakers kept coming forward, a group of chanting and yelling demonstrators jumped into the middle of the room with a banner reading “Equal Pay = Equal Work” before Metro employees and security staff shoved them out of the room.

Board members did not address the interruption, public comments or strike during the remainder of the meeting.

In front of a group of reporters afterward Wiedefeld said, “obviously there’s a lot of tension around the strike and around this issue.”

He noted that a federal mediator was working to bring both Transdev and the union closer to an agreement.

“Hopefully cool heads will prevail and we’ll reach closure on this very soon,” Wiedefeld said. “In the meantime, I’m not going to get into it because they’re in the middle of some heated negotiations, and I’m not going to weigh in one way or the other.”

Union members warned Metro that they would also demonstrate against the Silver Line if Metro privatized operations, but Wiedefeld declined to comment. He again outlined a point of view he has raised repeatedly to justify private contracts, which he said is common in public transit.

Metro’s annual operating costs are rising higher than its subsidies, and there are few options but to find ways to cut costs.

“My priorities are not to cut service or raise fares to the extent it chases riders away,” he said.

Outside, union members that had gathered after the disruption said Wiedefeld can expect the protests to grow louder and more frequent until Transdev compensates its workers as well as Metro does or until Metro rescinds its outsourcing contract.