You mentioned that recent C41 rolls turned out to be ok. Did you look at the negatives, or only the prints?
C41 can bear quite a bit of overexposure. I once shot a 400 film with 100 setting by mistake, and just looking at the prints I
didn't see a problem with them. Ok, comparing them with correct exposed prints reveiled that they are not as good, but
I saw it only when comparing them side by side.
So it could be the camera had the problem before and you just didn't notice it.