Have you really run a 36 exp. film through it every month? I think my Zenit EM, which I've had since 1979 has had at the most 20 rolls through it
In fairness, that's about at the point where you got sick of all of the quirks of Zenit's build quality
. I think I put about 15 rolls through my '11 (which was essentially just an EM with a new name, and a different lens mounting ring, iirc) before I got sick of it and upgraded to a 'proper camera' (a T70)