I have seized cup and cone bottom bracket, I don't want to damage the paintwork too much, so im going to try slowly slowly catchy monkey and soak it in penetrating oil, so what one is best?
Forget wd40 or gt85, they are not penetrating oils/fluids nor lubricants per se, wd = water dispersant. Iirc.
Run a scriber or other pointy thing at thr join to break any rust out of the way. You can use a short lengtb of inner tube to raise the sides of the bb to bathe it in fluid.