My "light duty" rotary (also a RCR1260) doesn't have a slip clutch, just an oft-breaking (because of me) shear bolt. Am I bad that I removed the shroud that was always in the way of replacing the shear bolt? Seems to me a superfluous bit of safety kit given that you shouldn't be anywhere near the gearbox when that thing is running!
I have a slip clutch on my heavy tiller and it obviously works because a, I catch a lot of hefty rocks when tilling new ground and b, my tractor isn't broken (yet). Definitely do the loosen the clutch and make sure it spins thing on that, though I haven't torqued it before - great idea!