Whatcha got in the syringes? I am just curious what people use in place of RC branded stuff. The blue stuff looks like what I use in my bearings... Maxima Waterproof grease.
You may have to adjust things on a maintenance routine as you go along and find fluids not as clean, or cleaner than you hoped for. My main concern is my RC's bearings, and shocks which get flushed/cleaned/rebuilt every 12 battery pack ran, because of the dusty (extreme?) track conditions...
I don't know that I've read Tekno specifically recommending changing diff fluid after a short term and gears have a chance to break in, but it's not a bad idea. I normally open up the diffs and have a looksee at the fluid after the first 12 packs ran through the RC. Yeah, almost always the fluid...