LOTSA prep req'd before you "seal" dirt, stains, old wax etc. The thread I read in history said to abrade the surface with Bar Keepers Friend which we did using a 3M composition "sandpaper" block...kinda like a "rust eraser" block. I forgot the name of this product...it's not sandpaper. The "Mr. Clean" abrasion sponge fell apart quickly so that idea was discarded. Used this block and BKF to remove peeling clear coat, marks, dirt...everything. Then washed area with 'DAWN" detergent. Everything allowed to dry then began applying multiple coats of ZEP. Remember what we're doing here...applying a SEALER to the surface. If you can see a defect then laying sealer on it will make sure it's preserved and visible. So...jus' like painting PREPARATION is EVERYTHING. It took wife several days to do the entire vehicle...doing a panel atta time. Do not apply when cool outside or raining. She hadda do a section over because ZEP wouldn't dry and turned to powder when she applied at 60 degrees and rain...but the finished product is gorgeous. The threads I read used Red Max or ZEP. They said they applied it once a year on an exposed vehicle. With mine in a barn outta the elements I expect much longer re-application requirements. If unsure perform the whole procedure on a basement door/cover or something. We're quite satisfied with the final result, the basement doors have clear coat peeling that I wanted to fix in the first place. Now I won't have to shoot paint for some time yet.
2014 XLR 415AMP, 2011 F350 6.7 DRW, restored 82 Wing, 02 Shadow, 06 ST1300A, NRA Benefactors.