Adhesion Promoter

I don't know about that primer, but one thing you can do would be to use fine grit steel wool or fine grit sandpaper to roughen up the paint that is there, to take some of the gloss off of it. Again, we are talking fine here, and fine steel wool is what you use between coats of varnish to allow the new layers to adhere to it. Potentially if you roughen the surface you may not even need the primer in question, if you use primer make sure to use a light coat of it. 

Think I will test it on some ABS plastic as suggested in previous "painting" postings. This would appear to be a good product for anyone wants a clear primer undercoat.

I stay away from any form of steel wool as it can leave tiny bits of steel wool behind. Might try a light abrasive cleanser  like "Bon-Ami".

You could also use those light abrasive pads like 3M makes to rough it up a bit. Remember if you make any deep marks they may show up through the paint like a bad chrome plating polish job.

If you are looking for an Etchant that will eliminate oils and the gloss, try soaking the part in white vinegar for about an hour or two and let dry. I have had great luck with this on repaints. It will also eliminate the worries of scratch marks from sanding.

I would second the suggestion to soak or at least wipe down with vinegar.  Alcohol can also be used; mostly in case there's any wax from the plastic mould still on the cars.  Even years later this can be the case.  I use a promoter on all plastics. ( Just a very light coat).  Last one was a new bumper shell on my wife's car.  Auto plastic painting requires a promoter.

Primers advertised for plastics simply have a promoter added in.

You could just buy a spray can of promoter at an auto paint supply store. 

Waddy,

I believe the product I mentioned "Dupli-Color Adhesion Promoter" is what your referring too. I bought it at an auto parts store.  It's Dupli-Color product CP199

The vinegar wipe down method sounds like a good process also.