Spirovent

My system has a Spriovent to remove air from the closed system. I had to drain the system partly to do some maintenance, and don't think that all of the air is out of the system. Normally, the vent can be heard exhausting air. The actual vent hole is covered with a crust and I think clogged - I can't hear anything and a couple of the branches of the in-floor heating are, I'm pretty sure, partly air blocked. The air vent in the boiler has been replaced several times too because they got corroded. I'm going to replace the boiler and hot water tank soon, and will have them look over an replace anything in the system that needs it, but would like this to work for maybe a month or so before that happens.

Can the Sprirovent be repaired or must it be replaced?