Belt dressing will remove glycol, and that is an acceptable use, but otherwise, if the belt squeals, softening it up temporarily is indeed a temporary fix, and will leave you without the belt sometime soon.

Serpentine belts very rarely squeal anyway -- they will run quietly in pretty terrible shape for a long time, the suddenly fly off when enough cording is broken so long as they are tight. Don't even squeal much when they are loose -- my brother heard a funny whistle from my 300D last years when he borrowed it while driving with the window down and smoking (the main reason I hate to lend him my cars!) -- the tensioner spring was MISSING and the AC still worked!

Squeals are usually a bad tensioner or a bad idler bearing -- they can whistle and growl, too.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!