I still have the original caps. I left them off as others were saying that the caps only trapped moisture inside and this was the cause of the corrosion in the first place. All 4 jack points had grease remaining with 3 of the 4 having corrosion at various stages. The corrosion was limited to the first inch or so inside the tube and the worst corrosion appeared to be at the outside edge.

I'm worried that putting the caps back on would start the process over again. Your idea of putting the POR 15 on the new corrosion seems logical although, as you say, care would have to be taken to avoid damaging the paint. I hope this would stop or substantially slow the corrosion.

Thanks for the response! I also appreciate all the others who have guided this repair.

Paul