About 6 months with the used VW now, and we feel it's a keeper.
So it had its first annual rust proofing. (We do that in the spring now, since that's when it's recommended I learned)
I am still loath to drill holes in German steel, so the request for no holes was made.
It was done by our local Canadian Tire (Corrison-free product) and we talked to our local branch to inquire about how they'd do it, etc. Technique is really often the most important thing. The manager and guy who applied the substance seemed to know their stuff, so we went ahead. The guy who applied it also said he would not drill the VW hatch either. He went through existing ports of entry. He did a great, we are pleased.
This is a recent pic at work where a colleague and I happen to both be working on-call and there was no one else in the garage. He has a Golf R. So they looked like "brothers from another mother"
EDIT: Sorry for the no flash. The Golf R is the one in the beautiful Rising Blue color.