Dab of RTV around rubber plug prevents this. Jeepers have been doing this for years.

 

.......or keep the RTV out of the diff and spendy the $3 for a new plug.

http://www.summitracing.com/parts/RNB-65293?seid=srese2

 

Or just buy a new heavy duty cover and never look back.

 

There's a Jeeper with plenty cha-ching.

 

It won't go in your diff. You can actually just dab the tiniest bit around the lip of the plug while the plug is still plugged into the cover. The lip will peel back just a bit. To each his own - I would think a new plug might not necessarily solve the problem either.

 

Usually, a new whatever fixes a problem......and $3 is mighty cheap for new.