How do you remove oil based primer from vinyl?

It can be sand blasted (at a cost) Burned off (hard work and can if the paint is old be bad for health) brushed or scrapped (hard work as not all will come off) However, you can paint a thinned down PVA over the oil based pain and then add a high quality wall paint 50 /50 (water and paint ) followed by 100% paint once dried.