I had a similar problem with a Betax 4 shutter just the other week. It worked when I got the lens - a convertible Velostigmat, but after just one tour in the forest it just didn't. And just as yours, times fired fine but B and T didn't react.

So I opened the front, just one screw; nothing. So I opened the next level, very carefully, fired the shutter a few times and; voila.
Still don't know what happened, maybe it just needed a breath of fresh air, a glimpse of a blue cloudless sky - or an eveningwhite ceiling. Anyway, It's definitely a mystery I can live with.

My point is, maybe nothing really happened, and if you look carefully into it, with the love and affection old things need, the shutter will understand that too.

Gr.