Well, I've re-lubed the motor, idler, and the main bearing and I can't hear the slightest bit of rumble. I've rewired the output cable, motor and switch. It's now fully earthed and a lot better insulated where mains exists. Stock Lenco arm now has new V blocks. This really rocks. I'm tempted with that AT3600l I have lying around too.
I'm torn between spending a load of money on a new plinth, cartridge and arm, or just enjoying what this [currently] bargain basement TT can do. Unfortunately I live in a rather wobbly floored house and putting a shelf up isn't going to be allowed so to enjoy it further I think it really needs a solid footing.
Next projects: Redesign Naim's 322 MM card for easy input capacitance changing, Martin's DC Motor thingy or a PSU rebuild on the RD11e, that active SBL crossover project...