I wouldn't say that a RMS that isn't leaking is necessarily "good". It's just a thin piece of rubber and, like all rubber parts, it degrades over time. It's certainly possible that it will never degrade to the point that it leaks, but given how hard it is to get to, and how inexpensive the part is, I think the cost/benefit heavily weighs in favor of replacement. For what it's worth, I replaced mine at 90k (with the clutch) and it wasn't leaking at all but the rubber absolutely wasn't as pliable as the one that came out of my father's R which had about half as many miles. The seal in the iABED kit is an objectively better part—it's made of higher quality rubber—and I don't see how this is the kind of part that I'd worry about breaking the factory seal (ha) on. But, reasonable minds can disagree.