Adam, TD, Can You Help Me?!

[HyperFX]

I purchased a used DEX410. I was told by the previous owner, the diff oils were 20K/10K. I drove the car for a few weekends, making only minor adjustments, because the setup was very good "as is".

OK, time for fresh fluids. I open the diffs to find...very little, and very dirty oil, or grease, in both diffs. No leakage at all, just under filled diffs, or small amount of grease. BUT, the car handled very well this way, although there was a little understeer in medium to tight turns.

I wanted to get rid of a little rear traction to increase my corner speed, so, based on the 20K/10K info I received, I went to 15K/ 7K. This produced very little rear traction. Now, I'm thinking increasing the rear diff to 10K or reducing the front diff oil to 10K, to regain rear stability. Is this correct, or is my logic "we todd did"? LOL! (Say it out loud several times!)
(edit: Now, I'm thinking thinner oil will increase traction/stability?)

I believe, now, that the 20K/10K info is wrong, and the car was handling well with low filled/grease only diffs.
SO...
How do I duplicate the good handling when the diffs were low? Thinner oil? Grease only? Help from the TD pro's?!

I don't have previous experience with oil diffs, (yes, it shows. duh!) and I'm in need of experienced racers help with this, please. I really need to know the basics of how diff oil viscosity affects the handling of the 410, both front and rear.

The track surface is medium to loose traction. Clay mix, partially packed, with loose, moist, soil on the surface. Moist during all heats and mains.

Adam, TD, or anyone, do you have a minute to educate an "oil diff noob" before I race in the morning?!

Much Thanks, in advance!