I've had two Synchro-Compur shutters that developed the low-speed paralysis, both Linhof lenses, if that makes any difference. In the one case, I sent it out for CLA and it was fine for the first three months, but after I had not used it for the winter ( about 6 months - this is Canada), the slow speeds became sluggish again.
I applied frequent exercise, just sitting there cocking and firing the shutter repeatedly while watching TV, and all speeds returned to fully functional after a couple of evenings.
The second lens was acquired at a flea market, stiffened up to a terrible state, and I was able to get that one completely functional with the same treatment of exercise, aided by an initial couple of drops of naptha (lighter fluid) and a blast of ether.
Both are still working fine, but I continue to exercise them regularly. That's been about ten years now.