Starter problem - '86 5TQ

[urquattro]

IME it is likely to be the starter (the starter and solenoid are
integrated).  While I believe it is possible to replace only the solenoid, I
think the common practice is to replace the entire unit.  I've dealt with a
lot of starter issues on Audis over the years (good grief, I've been an Audi
owner for 22 years now!) ... if you dig into the problem you'd probably find
that the ignition switch resistance and the resistance in the wiring to the
starter has increased which leads to reduced voltage at the starter ... but
that said, a new starter has always done the trick to getting it running
again for me.