I have the NV4500 tranny and NP205 transfer case.

How do you check fluid level? I have only checked automatics before. Get it hot, shift through all the gears. Check it while running etc...

Never done a manual tranny or transfer case.

The t-fer case has a leaky seal and I don't want it to dry out.

Also, is it normal for there to be some grinding when shifting into third? I usually happens when shifting fast/ high revs or when down shifting. The clutch is all the way to the floor when shifting too.

 

Park truck in a level spot (engine off, hot or cold is not important). Get the right size wrench (trans is 3/8 drive hole, Xfer case is a big hex head) and remove the fill plug. If oil runs out it is full, if not add oil until it overflows.

Sounds like the synchros are tired. Don't rush it, and double clutch on the way down until you get around to rebuilding the trans.