Gawd ......... someone must smoke a lot then Sir P!
Yes, laborious job. It needs to be cut with a sharp Stanley knife and peeled back. There are special removing chemicals available, but they're really only suitable for the last traces........... unless you stand there all day applying coat after coat.
I have a pet hate ..... that hideous Brilliant White that PVC comes in. Eventually, that also discolours.
I use PVC a lot, but always paint it (inside and out). All you need is the right primer, then regular paint in a colour of YOUR choice. Sooo much more sophisticated, befitting a man of your calibre ;o)