I've got a 17 RR 250 and okay I bought it used in June. I feel your pain and am living a similar nightmare. Another Friday bike. Its currently sat waiting for a new cdi as its delaminated and causing running issues. A new tank as it leaks where its moulded for the tap. It's only just had a new stator as the old 1 had corroded and was causing starting issues(not covered under warranty as it had gone rusty). It's partly melted the water pump impeller(metal insert is all loose with the recess in the seal full of melted plastic)where it boiled over due to yet another thermostat failure another impeller just split. Noticed the Bush in the chain tensioner goes very easily aswell.
It did sieze once aswell (sort of my fault, no lanyard) but that was down to previous owner not seating the o-ring on the thermostat correctly n the coolant dripping out. I never noticed the loss of coolant and had a off. It seized in a few seconds without coolant and broke another impeller
Tbf when it runs it grips n rides lovely but seems everytime it comes out to play something goes tits up on it