I have now put the UV lamp flatter and closer to the paper, probably at around half the distance now, so my exposure times have dropped, i'm gradually working my way back to correct exposure, each one takes around 10 minutes now which saves time and bulb life!

I have some transparencies on order, will be interesting to see what the exposure time is on those vs oiled paper, I might also look into creating a larger UV box with longer tubes so that I can do more than 1 print at a time - I am currently exposing 2 x 1/4 A4 prints in an A4 clipframe which seems to be working out well. I doubt I will be able to go an larger than A4 though due to not being able to print any larger than A4.