[Mouton]

First off, you are in The States, I thought Tamiya America was an active distributor that always carry a good stock of parts? Most replies seem to refer to the UK.

Here is my input to your questions:
1. Yes. A solid yes, even. I live in Sweden and have no real problems getting parts (the few that break) from our distributor. In the rare case they cannot help me out urgently, Vellrip Stella Models on eBay can. Ask Tamiyausa for a hobby shop that carries a lot of parts and you should be good to go. Come to think of it, can't you order parts directly from Tamiyausa.com?

As for quality, I would say it is top notch. Every car has drawbacks. The 511 is no exception, but that does not make it a bad car. If you where to wait for the perfect car, you will never be able to drive. A good car is a car where you can live with the kinks. It is easy to change them on the TRF511. I prefer having it the way it is rather than have a car where more expensive parts are troublesome. Look at Durango and their wheel shafts...

2. I have changed the following:
42142 TRF 3mm Ceramic Diff Ball - two sets required
53969 Hex Head Ball Connector - two sets required
They are the parts that need to be changed. The rest you can deal with if you break it.

My car also has:
53961 Aluminum Caster Block
53962 Aluminum Rear Upright
54121 Aluminum Horn For Hi Torque Servo Saver
53971 Aluminium Steering Arm
53972 Aluminium Steering Bridge
53973 Aluminium Steering Base
42117 turnbuckles
42118 turnbuckles
42121 turnbuckles - two sets needed
53963 Stabilizer Set
aluminum servo stay I do not remeber exactly which part no but can check.
Alaste's front and rear diff covers
Alaste's LiPo tray
Most important upgrades to me are Alaste's (Fredrik Emilsson here on Oople.com) front and reaf diff covers. They are a must for a dirt track. Alaste has also made a LiPo-tray that is better than Tamiya's. Lee Martin and Viktor Wilck also use the Alaste parts.

The next time I will tear the dampers apart I will use these to replace to stock red parts:
42137 Competition O-rings (damper parts)
The brass parts that replace the stock plastic parts for the upper shock mounts (the part between the shock and screw that attaches it to the shock tower).

Good spare parts to have:
51271 B Parts (wing stay)
54131 C Parts ()
54034 D Parts (unless you go for aluminum caster blocks)
51274 E Parts (unless you go for the aluminum rear hub)
54141 DB01 High-traction Lower Arm (Front)
54142 DB01 High-traction Lower Arm (Rear)
54140 Drive Belt
51314 Spur gear 91T
53989 Pulley
51287 Diff Plate
51287 Ball differential Pulley 37T
4304094 Front Damper Stay (front shock tower)
4304095 Rear Damper Stay (rear shock tower)

Apart from the Tamiya body, Team Azarashi also make a body that fits the TRF511.

Hope this helps!
Andreas