BSR Turntable

Ok I've had a missive amount of trouble trying to find a replacement belt for a turntable I inherited It's part of a Bush tower system (model number 8890) I have the manuals with it and the Turntable operating instructions are for a BSR P280 & P287 I'm guessing it's the same model just one is for the stand alone. My issue is nothing in the booklets tell me the belt size. I've tried the "Fits most BSR models" belts 121mm diameter ones. It's too tight causing the speed to slow up and stutter at 33rpm. The belt I took off originally measures 420mm long 6mm wide .5mm-ish thick.. I believe that works out to be 133mm diameter, but I can't find a belt even close to them dimensions. They are either much smaller or larger still. I've tried the soaking the belt in hot water for 10 min to shrink it back to original size to remeasure is but it made no difference. I'd like to find out for sure what this models belt size should be before looking at the motor as I'm a little unwilling to potentially break it on a whim.