Fix Thorens or replace?

By all means fix it if you can. The Thorens TD 166 Mk II, though not by any means the top of the line, can sound quite respectable with a little work. Check out
http://www.theanalogdept.com/thorens_dept_.htm
for some ideas.

Depends on how much "fixing" it needs and the cost of fixing it ( if you're not doing the work yourself. Some vintage tables just get old (like people) and don't operate as they did when new. Might be worth picking up an old AR XA, Dual, etc cheap and run it into the ground.

Almost all Thorens turntables are virtually indestructible, and since your turntable is a belt drive model, I suppose a simple fix in lubricating the inner spindle rotating parts and putting a new belt might be all that you need to do. The rotating parts of the arm should also be lubricated using a light lubricant such as WD40. In my personal experiences with many Thorens models, I have temporarily used the longer red rubber bands that you can purchase in the large office supply stores such as Office Depot. They are seamless and work rather well for as long as you don't have to stretch them much more than a factor of two. Then you can shop around for a better replacement belt priced reasonably without having to panic for a quick replacement at any price. Long live your Thorens!

Thanks,
I think I,m going to try to fix it.
John