After reading John Tuttle's good post on PVC-E, I would simply add that
for PVC-E, the recommended solvent is acetone.  The recommended method
is mechanical -- scraping.  Also, generic PVC thermosetting elastomer
should soften at 140 degrees Fahrenheit.  (And is likely to get brittle
around freezing.  But then, I get brittle at that temperature, too!)

Respectfully,
Wm. Grant Chapman
West Point, New York