Platter wobble


I have a Technics SL-BD20D and the platter has a noticeable wobble while spinning. ive tried a couple mats - cork and acrylic - which made the wobble much more apparent.  The rigid acrylic platter would not lay flat on the platter. 

Anything I can do? Is there a way to test what the issue is?  Is there an quality aftermarket platter that I can use?

Thanks!
leemaze
Dear @leemaze: What are you waiting for ? , just from the very first post in your thread @noromance  gave you the rigth answer, now it's up to you.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.
The OP has a belt drive turntable with a cast aluminum platter. The turntable’s prior owner(s) probably bent the platter by pushing it down one one side. These platters aren’t designed to withstand that kind of abuse. Given what it is, the OP could try to “correct” the bend in the platter by rotating it to the high point and gently pressing down until it turns without significant runout. Bottom like is these things are a dime a dozen, easily damaged by carelessness, and the p-mount cartridges tend to be lacklustre. With that said, a well cared for turntable similar to the OP’s turntable can produce much better sound quality than its value would suggest. 
Fingers crossed. If it is, put it on a stable table on a sheet of granite and treat yourself to an Audio Technica AT95E cartridge.