I have a '93 4Runner 22RE with 4.10s and I just picked up a complete 4.56 front diff and and rear third. The seller recommended I clean out whatever crud there is inside each unit before running them to freshen them up. Is it worth the extra work to do this, and if I do, what's the best product/method to use?

 

Have they been sitting out in the weather open? Not really sure what "crud" would be in there.
You could run then and just change the gear oil after you get about 100 miles on them to do like a "flush".
If they are full of dirt or something definitely clean them out first

 

The front I believe is factory sealed, and the third looks to be in good shape. I don't want to do the extra work so I agree with you. I'll probably flush them with fresh gear oil.