What about rear hubs, caster blocks and steering blocks? After trying different plastic and aluminum ones from integy, rpm, and several other companies, those parts I would only get from Traxxas, along with the aluminum steering bellcrank. I'm currently working on a Slash that I did that upgrade to with TRX parts, just because that's one thing Traxxas did right, along with the steel driveshafts. Even the stock plastic bellcrank is better than most aftermarket aluminum ones that are available. As for arms, I prefer the TRX HD ones over RPM. They break way less in extreme conditions.
Disclaimer: I personally hate giving any money to Traxxas, but, after owning 4 Slashes, 4 Stampedes, 2 Bandits, and 2 Rustlers, and trying every aftermarket parts, from every company available, even the stuff on eBay and Amazon, I have learned that there are some things that only Traxxas has done right.