I read up a bit on the crankcase venting and thought there was a chance that plumbing it into the carb would help. Plan was to do the plumbing, clean up the engine, go for a drive and see where the oil comes from and hope that the breathers sort it out.
Just done the piping, took the car out of the garage and there's three small pools of oil on the garage floor, so it's not pressure forcing the oil out, a constant low-level drip, drip, drip instead. Bummer.
So same plan, clean it up and see where it's leaking, but looks like I'll be replacing a few seals!