I bought a used 2009 Pontiac torrent with 104000 miles on it in spring of 2018, it is a great looking and good running car, it had some oil leaks and my wife took it to the shop to have it repaired, it was the oil pan gasket, the repair was completed with great difficulty, according to shop owner, due to excessive under body rust. the owner informed me that the frame is rusted pretty badly near the motor mounts, my question: would it be worthwhile for me to take the car to a rustproofer to attempt to stop any further damage to the frame? I live in Columbus, ohio where salt is used liberally on the roads in the winter. also the car was originally titled in Canada.
Too late , the rust has already been formed . I think you should pay a good body shop to look at this to see just how bad the rust has compromised things.
some cars are prone to subframe rust for whatever reason. that does not mean the unibody is toast. a big problem is getting the subframe bolts to come out without spinning the captive nuts inside the rails. any trans shop could drop the subframe as that is step 1 in pulling the trans. get a good used subframe.