I've had similar platter wobble issues on two Well Tempered Simplex TTs with the triangle top bearing.
If the platter spindle isn't placed exactly in the centre of the bottom bearing well, the platter wobbles like crazy and I can see the actual spindle rotating off centre.
If I lift the platter out and reinsert it holding it only by the top of the spindle so it effectively hangs straight down, not by holding it on the sides, I can get the platter to be wobble free. Sounds strange but the manual says:
" It is most important that spindle is located correctly in the centre of the lower thrust bearing. Failure to locate the pivot point of the spindle correctly will cause the platter to rotate abnormally. The spindle has been designed to protrude through the platter to provide a central lifting point that enables the user to easily achieve this".
Maybe this is what's causing your problem?