Just had another thought or two! It might be worth checking the bushing of your idler wheel (check for flat spots as well), and stripping and refurbing your motor. Both excercises are useful in stopping vibration getting into the platter.
PS I think you've been really smart with the choice of materials for your platter
SS
CD Teac VRDS25X(Audiotuned) DECK 1210 Mat Crystal Audio Mods MN Base/Bearing/Platter+Ebony armboard Feet Isonoe PSU Paul Hynes SR7EHD-27XL/DCSXL Ag DC lead/3 Stage Regs/Recap PCB+No Pitch/Strobe/Light ARM SME V(Kondo Ag Rewire&Tags) MC Cadenza Black FGS CABLES Arm Yannis SPD-4 IC Yannis 222 Litz+Ag bullets Power WAR PRE ATC SCA2 SPEAKERS ATC 50ASL STANDS Atacama PHONO Sugden Masterclass PA4 SUT Ortofon ST80SE POWER PSAudio P10
VALVE
PRE Croft Epoch(Modded) AMP Sondex S100 (Modded) SPEAKERS Tannoy 15"MG+RFC Warwick cabs+ Ref XO + Batpure supertweeters DECK Garrard 301 Mat Teunto Bearings 401(Bastin) Plinth Bamboo Arms 3009/3012 PSU Eagle+Tachometer MC Ag Meister II/FGS + Ortofon SPU MONO CABLES Arm Yannis 420.5 Litz+ SpeakerPC Tripple C+WBT-0681 Ag IC Oyaide FTVS-510 AgWBT 0110Ag Phonostages Paradise(4 Box Mega-Modded) / Croft Musicmaker
MONO
Pre Croft Epoch Power Sondex S100 Deck Garrard 301 Tonearm SME 3009 Cartridge SPU MONO mk II Phonostage Croft Music Maker Speaker Quad ESL 57 Cables Tonearm SME IC - Duelund Realsound Speaker SEAC 850C