RK 55HC,ym1700, NH7610S, Ford 8N, 2N, NAA, 660, 850 x2, 541, 950, 941D, 951, 2000, 3000, 4000, 4600, 5000, 740, IH 'C' 'H', CUB, John Deere 'B', allis 'G', case VAC
I'm not familiar with the pto setup on that 3600.. but if a manual engaged system, is there any in/out play on the pto shaft? if so, it will walk a manual engagement out... and eventually chew the collar and shaft end.
the play is usually abearing or snap ring or damaged carrier housing.. etc.