Auto body repair & detailing: Lift-gate rust repair, dodge minivan, rust prevention

Question
In Septmeber 2005, I had some rust repaired on my 2001 Dodge minivan.  The seam at the bottom of the lift-gate began to rust and I wanted to limit the damage.  I had the repair completed by the dealer that sold me the van.

I recently noticed the seam is rusting again and the body shop has indicated they do not guarantee any rust repairs.

I feel the repair should have lasted years, not months. Any advice on how to proceed?  

FYI - I live in Michigan and the van gets plenty of salt in the winter.  I have van washed regularly.

Answer
Well, I hate to be the bearer of bad tidings, but most body shops do not guarantee rust. Unless you forked over big bucks and paid to have the bottom of the gate patched, the repair will only last maybe a year. Did you have the gate professionally undercoated after the repair? Or perhaps hot oil treated? My guess is no. 99% of owners fail to follow up with rust prevention after the repair, and it's why the repair usually fails prematurely. Thats why we don't guarantee rust. My suggestion? See if the shop will give you a break on replacing the gate with a clean used one, or a break on patching the old one. Have them recomend an undercoating service, and follow thru on it. Wish I had better news for you, but rust is the most difficult damage to repair. Your best bet is to replace the gate with a rust free one, and have it professionally undercoated with parifin based undercoat. It has an amber color to it. The black stuff is crap. Bill