Removing oil paint?

I've been thinking about redoing some earlier sets of mine which clearly deserve a better paintjob, now that I have improved a lot (and learnt from those many mistakes). Spending already a smaller fortune on newly acquired boxes (so much temptation!), I finally decided to remove the paint, but hitting the topic in google I found various results and opinions. Here's the question: does any of this blog's readers have experience, and/or could you recommend a safe way to solve this problem? It's Humbrol/Revell oil paint+varnish on plastic in every case.