Just bought a 1998 ranger 4wd with a 3.0....172k miles
Has a Mazda d50 manual

I rebuilt the engine....put it in last night.
No oil in it. And still not hooked up. It has two bolts holding it to the transmission at this point.

Reason I'm here is that the bell housing was black. Caked oil and grime covering the entire housing. I cleaned it up and thought nothing of it. Now it's nice and silver. Did not inspect anything before putting the engine in.

The engine was pretty hard to get in. Took 4 hours to line it up. Clutch was straight.

When I got the motor in I noticed a drip coming from the rear main seal area......right around where the throw out bearing is. It didn't drip but it looked like fresh fluid of some sort. What could this be? Leaking slave assembly?

It's not common for input shaft seals to leak...
I've never driven the truck so I'm not aware of any problems. The fact that the bell housing was oil black leads me to believe the engine should come back out and closer inspect. I'm not familiar with the drive train of this truck. But I really don't want to pull that engine again. I felt lucky to get it in. Had my fair share of manual trans engine installs. This one was the hardest for some reason. I expected it to line right up.

I did re grease the pilot bearing.

 

That drip was sitting on the blue part of the slave cylinder. I wonder if it's leaking brake fluid.
The throw out bearing was very smooth
It looks like it's connected to the slave cylinder so chances are it new. What is leaking?

 

Has an M5OD-R1 it it is a manual trans, 1990 to 2012 all Rangers/Mazdas used these.

Trans has AFT inside so fluid would be Red.
Yes, manual trans that uses AFT..............

With no oil in the engine then all that is left is brake/clutch fluid, not sure how it would get there?

You could hook up the quick connect and pump the clutch pedal a few times