1990 4000 80 sedan spark plug wire boot removal

[TEX TERRY, II]

The spark plug wire boots, on the spark plugs, and on the distributor cap,
seem to be stuck on.  Don't want to pull too hard to break something.  Do
these twist off, have some kind of locking mechanism, or are they probably
just stuck from crud build up?  This is on a friend's 1990 Audi 80 4000
sedan (non-quattro).  Thanks in advance for your help.

Tex Terry, II
83 5kt sedan (non-quattro)
Franklin, PA  USA