Originally Posted by justpoet

You should change diff fluids and shock fluids at least occasionally. The real answer is "when dirty", but you can't see in there to tell when that is. If you're a top racer, you change them all the time so it is super consistent and always exactly the same. If you're not a top racer, that matters less, so you care about mechanical wear and tear. For shocks, if you run boots and they're not torn, you can keep the same fluids for a long time and they'll still come out clean on the Tekno shocks. But if the boots aren't on, or get torn, etc...replace the oil as you fix that and clean the orings in the cartridge. Try changing this at the one month mark if you don't otherwise notice air in the shocks or leaking, and if the fluid is still clean, go a little longer the next time, etc.

Diffs are similar...but there are 2 key things to keep in mind.
1) The first time you put them together, you should then do a break in, which WILL dirty the fluid some. So, change diff fluids after the first or 2nd pack, or at least after the first track day of use.
2) The SCT runs composite cross pins in the diff out of the box for less rotating mass and performance. If you run these, you should probably stick to the roughly once a month or every other month diff fluid change (assuming you run at least once a week for any period of time). However, if you're running one of the metal cross pin options...it is still a good idea to do that...but you can go a LOT longer and as long as the diff still feels like it has resistance (so it isn't empty) and is smooth, you probably won't hurt anything by running it (I once did a year + and only took one apart to change the worn out outdrives, just to see if it would do it, and it was fine...but don't do that).

Fluid maintenance is something that matters more, the more your vehicle being EXACTLY the same matters to your racing skill level. If you can't feel the difference in driving it on the track yet, just worry about making sure it stays in good shape, and you'll be fine. Other vehicles that aren't Tekno often need more frequent rebuilds of things like diffs to not leak out their fluid, or shocks due to not sealing out dirt as well, but the above general rules about cleanliness of the fluids should still apply.