I personally haven't noticed any bind in the rear dogbones unless I accidently put it there.
I originally tried to put too many 'fillers' in the outdrives and axle cups so there wouldn't be any 'float' in the dogbone at all (It's been awhile since I've had dogbones in a car). That of course didn't work and caused some major binding issues. I'm not too keen on getting the rear universals when they cost 37$ US (probably a lot more for you UK folks) so I figured I'd try to make the best of it with the doggies. I've found that if you stick only 1 Losi shock o-ring in the diff outdrive, it seems to give just enough float to the dogbone yet at the same time not bind the suspension at all, or at least while it is stationary. I'm not sure how much binding occurs when the car is actually in motion and the suspension is working. Also, using the Losi shock o-ring allows for for diff adjustments without taking them out since you can stick a wrench through the o-ring.
I still haven't gotten around to changing out the springs, but then again, the American tracks I run on usually differ a lot with your UK tracks. After changing the shock oil to 35wt in the rear and 40 up front, I find there is minimal body roll in the corners and the stock kit springs still have enough speed to return the tires quickly to the ground through the bumps without having the car getting tossed after the second bump or so consecutively. I'd like to pick up some stiffer springs though to try out different setups I might like a bit more from the current one I run.
Simon mentioned problems with spur gears. That is puzzling to me.... I haven't had any drivetrain problems other than the ones that have been caused by my own doing. I've unfortunately set my slipper too tight a few times and have blown out the rear diff gears, but I've yet to have a problem with the spur. In fact, I've been very impressed with the quality and precision of the drivetrain. It moves very freely and smooth. It's actually a lot more quiet running around the track than other 4-wheelers. Simon, if you don't already, I'd suggest checking your gear mesh all the way around the gear. I've noticed that the gear mesh is loose in some areas and tight in others. I try to find those tight areas and make my gear mesh adjustments there, and then work my way back to the looser areas to make sure it isn't too loose there once I've made an adjustment.
Lastly, I'd like to express my own personal dealings with "design flaws". It's been discussed many times already about the front brace so I won't get back into that here, but there are other things I thought maybe Kyosho could have done differently. The build of the diff cases seems a bit much. Too many screws and they aren't easily accessible. I'm also not a fan of the shock tower mount and camber link brace that both screw into the diff case. Seems excessive in my opinon. Why not just screw the shock tower and ball studs for the camber links directly into the bulkhead? Maybe I'm missing something? Also, changing the ballstud location for the camber links is a chore. you have to remove the shock tower to get to them... or at least I do to reach them with my current tools. I'd like to get the Losi titanium ball studs so that I can use my hex wrenches to reach them. Also, did Kyosho make a mistake by doing too good of a job in making the car so light? It hardly leaves room for optional carbon graphite pieces or the new woven carbon fibre pieces Jimmy just did a review on. The ROAR rules put 4wd max weight at 3lbs. 12oz. I have all stock pieces on my car with the exception of the titanium screw kit, and I'm at 3lbs. 12.1oz. Titanium turnbuckles or the new shock towers/center brace would put me under! I'm not a big fan of gluing or taping weights to my car to stay legal. I never know the best places to put them to keep things balanced. :wink: