First thing to do is download the owner and service manuals available on this site.
Just click on the "Library" on top left of this page or consult the "Reviews" over your Dual model.
Looks like your issue was quite common, but my personal knowledge of these models is somewhat limited (electronic speed control), my Duals are still the idler fully mechanical ones.
I'm sure Klaus or another of our Dual specialists will chime in, but it is always best to have a maximum of doc on hand.
Dual 1019/Shure M97xE/Jico SAS stylus + 1219/Shure V15 III + 1225
Thorens TD 146 & TD 166/Ortofon OMB5 and OM40 carts
Marantz Mod 6170/Marantz E 5000 cart
RCA 45 J-2 RP 190 record changer (1952)