Tranny Cleaning (inside)
 

Noob question here.
I am in process of rebuilding a bent rod engine. The block now has forged parts, is machined, and I am putting it all back together.

I noticed the inside of my tranny is quite filthy. I think it may have been from a slow leak on my slave cylinder (since fixed).
My neighbor says I should just degrease and clean it out, but I want to be fully sure. Any thoughts on if I should clean the inside of this bell housing and if yes, any specific advice or things I should be careful on?

https://cimg2.ibsrv.net/gimg/www.mia...40e1e3be73.jpg

Just many cans of brake clean. That's not your slave though, that's either rear main or input shaft seal, coupled with a little throw out bearing grease and clutch material.

Remove TOB, fork, and boot.
Install a thick plastic bag (ziplock freezer bad) and seal it to the TOB sleeve. (tape, big rubber bands)
You can use multiple cans of brake clean but I usually hit it with a pressure washer first.
After it's minty clean remove the front cover and replace the transmission front seal and gasket.
Use Mazda OEM parts if possible.

If you hit with a heat gun, then use Gunk engine cleaner, it will wash right off.

I have cleaned so many of these, Curly's simple approach works just fine. A pressure washer if you have one, but you will still end up scrubbing away with paper towels and break clean. Unless you have strong evidence the oil is from the input shaft seal I would not replace it. They last better than most seals, by far. The rear main is a more likely culprit, and you are building a new engine.

You are all amazing. Thanks for the sound advice. Lots of cleaning in my near future :)