When you talk to TNF, be sure to tell them the age of your tent. There is the "old" North Face and the "new" North Face - I think they carried over the product names, but the build may very well be different now. A tent as old as yours may take the polyurethane based treatment because it was built from different materials than the current version of the tent (which is what is described in your link.)

Also, if you got soaked "a few years back," the situation won't have improved with time. The seams may not only leak, but the fly material may be wearing out which increases the chance of a tear under tension - and no amount of waterproofing treatment can help that. The advice to simply get a new tent might not be all that bad.