I have found that when all else fails, and they sure do--plain ol rubbing alcohol and some cotton balls will remove any hardcore tree sap, just wipe in swirling motion, not too fast, requires a little patience.
It dries quickly, and, if there is a a white film left over, don't panic, jsut wipe with a clean cotton cloth with more alcohol.
Must be done on cool surface, away from direct sunlight.
Works every time.
1995 MB E320 Wagon
2001 BMW 530i
2007 MINI Cooper S (!)