Try some Gun-Kote- mil spec, weapons grade, aerospace coatings. Better than powder painting- won't fade, resists paint strippers/acetone. Designed originally as weapon coatings for US Navy SEALS- required something like 300hrs of salt spray, then full auto weapons testing. Great stuff. Glass bead the steel, use their bare metal etcher, spray paint, dry, and bake in an oven for an hour at 325F. Can only be removed by sandblasting. Multiple colors. No affiliation. www.kgcoatings.com
I think I have that site
'87 D110- 300Tdi
ps- if you don't want to go that route, get some Dupont Etch Prime- VERY nasty stuff to breath- wear a breather painting mask- even outside. Great stuff. Then paint over- I highly recommend SEM spray paints if you are not gonna use a paint gun. At your auto paint store. IMHO- the SEM paint cans don't clog, and run until the can is empty.... for plastics, use SEM spray Adhesion Enhanser for Plastics, then top coat with SEM Paints. Again, no affiliation- just 40 years worth of turning wrenches on Porsche 911s.....