Has it seriously taken you 8.5 hours to service your cars after two runs!?!?
Ive had mine since October last year and hardly spend any time maintaining the car at all. I race once a week almost every week and the only real time i spend preparing my car is on the day of the race.
As for the diffs leaking you need to build them correctly making sure you use plenty of grease to seal them up, i use waterproof grease and have had no problems with diffs leaking. Ive gone at least 4 weeks without touching the diffs and they have stayed leak free during that time. I tend not to go 4 weeks normally though as i often change diff oils as a tuning option.
My previous car was a Losi xx4, now thats a car that needs constant servicing! I stripped a belt and did a spur gear in one meeting, good job it was at a national as it took me nearly an hour to replace the belt, then another hour to replace the spur after my secon race. Thats one of the main reasons i switched to a Durango and a wise decision its turned out to be.
As long as you keep on top of things on the day of racing you really shouldnt have to do much servicing during the week. Most problems occur due to parts not been put together correctly, if they are then potential problems are kept to a minimum.
As for the shocks ive only changed oild once since i got the car and thats mainly due to what Adam said, when i did go to change the oil it was completely clear!! Shock boots work wonders.
Not sure what surface youve been racing on but if it took you 2 hours to clean the car it must have been a mud bath! lol
Craig Collinson