So early this morning I go outside and notice there's a wet area beside my pool. The pump is leaking water. Fantastic.
I do some quick research and it appears to be likely either the mechanical impeller seal or the diffuser cap gasket. Either way, I have to disassemble the pump. So I order the go-kit off Amazon (yay for free same day?), get home after work and start tearing it apart.
TL;DR: whoever had last maintained the pump is an idiot. The wear cap on the impeller shaft was on backwards, there was apparently lube on the ceramic seal and well, yea. Unwired the pump, removed the motor from the housing and cleaned everything off. New seals went on great, gasket was indeed brittle and reinstalled everything in about 2 hours of work. Turned it on and now I'm kind of puzzled. The pump works way better than before the seal failed (I guess proper maintence will do that) but now that it is throwing more water, I'm getting aeration in my in-floor pop-ups for the first time since I've owned it. It seems like it's got so much more suction it's actually pulling the extra air out of the system - but I'm not sure if that means there's a leak elsewhere, like in the PVC connections on the older pump.
The in-floor isn't functioning right now because there's no valve gears in the housing so it just returns water to all zones at once - I'm thinking of fixing that now that the pump is actually moving water so much better so it seems like it might actually work.