pbekkerh wrote:Good idea.
While you are at it, couldn't you find out how much current is used by the Valve motor normally and when blocked and design a protection circuit, so the transistors won't burn out again.

Do you have any tips on how to remove the rubber compound ?

When I get it working I'll measure the working amps and stalled amps to see what it is but I have a feeling it is only small. trying to stop them from burning out will be near impossible but you could put an L.E.D on the instrument panel with a circuit to switch when the servo is pulling more than normal amps, this would then prompt to clean the power valves. Best I can think of but I'm not an electronic's fundy!
To remove the rubber compound just takes time with tweezers and a sergical knife being very careful not to damage the board from what I understand, will let you know how it goes.