sealing up a pinion diff

[Lowie]

I have an E-Firestorm 10T.
It is an electro truck but it has a pinion-diff, as do most Nitro cars. Actually, this diff is the same as the one in the (nitro) Firestorm 10T.
Originally, this diff contains some grease but this is quickly swepped to the sides, making the diff run very smoothly.
As this diff is the same as in it's nitro brohther, the diff can be filled with diff-oil to tune it up.

I actually filled mine with 5000 oil and this improved the handling very much when driving on a grass track in my neighborhoud.
But, unfortunaltly the diff case washer has a little crack in it and my diff leaks out this diff-oil.

diff case washer


I tried to order a new silicone-diff case washer, but my local dealer had difficulties getting it. Strange thing!
But in the mean while, I have to clean up my truck very regulary and have to open up the tranny and diff to add more oil.
Are there tricks, you Nitro-guys use to seal up the pinion-diff? I tried applying some green slime, but that didn't stop the leaking.
I was now thinking of making my own washer.

Thanks!