RTV is a type of sealant in a tube you apply between the shifter and top of the transmission so the oil inside does not leak out between them. The B&M instructions say put it on the bottom of the shift kit before it goes in -- but you're better off putting it on top of the transmission -- because you know you've got it in the perfect spot that way.
Have not driven a GMM equipped car, but the B&M is far less expensive and they're based in the US in case of a technical problem. The GMM has a shorter stick -- but you can easily modify the B&M to equal that. The B&M is also a heck of a lot easier to install, too, as you're not fiddling with another set of hex nuts on top of the transmission -- that are positioned under the floorpan.
Regarding the Loctite, yes, it HAS to go on ALL the bolts, even the B&M tightened ones on the stick and base. I believe the problem the 05GOAT ran into is that he used a product similar to red Loctite -- as opposed to red Loctite itself. While these products look the same, they don't perform the same.