The rubber hardtop seals are capable of lasting (as seals) for over 20 years, but
The MAIN degrading environmental effect on this extruded rubber is--SUN/HEAT/ULTRAVIOLET-
If you leave your HARD/SOFT tops off ALL SUMMER, without protection from the sun-their active life is severly diminished-
The hardtop seals don't NEED any treatment, other than protect from sun/don't subject them to any odd shape pressure/don't allow any oil (type) to stay AND BE SURE THE MATING SURFACES OF THE TOPS ARE CLEAN/DRY-
Vacuum and warm water wipedown, before reuse and they're fine--water leaks are at CORNERS/JOINTS that aren't properly mated/maintained/replaced !!
Keep yer powder dry !