I was already thinking on these lines. Despite the fact that I would have tested it on a small scrap of mylar, I was very wary also about using alcohol or strong cleansing products.
I had the front glass (actually plastic) of my Swatch watch become completely opaque (cloudy, white) from cleaning it with regular pharmacy alcohol...
So I've already had some bad experiences.
I will try olive oil (very common here in Barcelona) and then a bit of lightly soapy water to leave the surface clean to accept the new adhesive of the patch.
Otherwise, if I only use the oil the new adhesive would also be affected and the patch would not last long...!