Finally got my S10 back on the road. As I said before, I bought an AC Delco seal from the Chevy dealer ($17). I used a 1 1/2" PVC coupler and rubber mallet to pound it in; perfect diameter of the coupler to fit over the seal. I then had to buy a set of HUGE allen sockets from Craftsman. I needed a 17mm allen socket to get the fill plug (and drain) out of the transmission. I then used a hand pump to pump 1qt of fluid in for the time being (could not properly fill it due to the truck being not level). I found no where that stated what size the fill/drain plug was which really made it hard to guess what size to buy.
Does anyone know how I could do a write-up that could be found by using Google? I'd like to make one stating what I did and tools used for anyone else looking.
You could've asked me and I'd have told you...
4.3?
Then you'll have the 8.5/8.6" rear diff... Or you should, anyway...
Rear diff check plug is a 1/4" ratchet...
13mm bolts to take the diff cover off.
I wasn't working on the rear diff. I was working on the transmission (NV3500).
Wait...I'm supposed to have a 8.5" and not a 7.5"? I thought S10's came with 7.5".
So far, after 70 miles, no leaks on the seal....but I think there is a leak from the shifter. That'll get looked at some other time.
I know... I'm just giving you a heads up when you go to do the rear diff

I've got the same transmission
'98 + S-series vehicles got the 8.5" rear end with the manual transmission... It's easy to tell from looking at it, but if you check my pic I posted, you'll see the tabs on the bottom are flat, instead of pointy... That means it's the 8.5...
5-speed 4.3s also got the iron front diff instead of aluminum...