I wouldnt worry about the shifter seal or the neutral switch unless you need to replace them. If you were gonna buy them and you werent gonna buy them locally Id buy from rockymountainatvmc.com. The oring for the oil cooler should be the same. I have an OEM one in my oil cooler.
When I stripped out two of those screws I just drilled the heads off, removed the plate, gently tapped on it, and backed it out with a pair of needle nose pliers.