I've used silly putty in the diffs of my formula off road truck with great success. I just stuff the diffs as full as I can. On road may be different when you need consistant handling. Eventually the putty turns into a syrupy goop that does kind of flow back into the gears. It may be worth a shot.
I have had great luck with cleaning putty. It is pretty consistent from run to run and within a single run. I ran my putty filled diff through the entire Reedy Race, a couple of test days, and the entire ROAR Nats with no difference in feel.
all my buddy packed the gear diff with grease (Heavy Equipment machine Grease) on their 1/8th buggy center gear diff and it holds up without slip. I say this should be fine when using it on the front gear diff on a touring car but I haven't tried it myself.
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