Toyota Repair: 86 Toyota PU 4x4 leaking heavy (90w)? oil out of front end, pinion seal, correct tools

Question
I bought an 86 toyota PU about 6 months ago... and it has needed a lot of help.  It has 249k miles on it, and I have replaced the Timing chain and cover, the head, the thermostat, water pump, and a few others.  I have recently noticed a considerable amount of heavy oil, I assume it it like 90w or something.  I am judging by the smell.  It smells just like grease.  Anyway.. I was wondering if it is a difficult repair to tear into the front end and replace the gasket, or is it something else.  I am just a weekend warrior mechanic, with an internet connection, so any real-world advice would be great... Thanks

Answer
There are two possible causes for the leak, one of them is the pinion seal where the driveshaft enters the differential and the other one is the housing gasket, neither one of these rerpairs is exactly an easy task, to replace the pinion seal the driveline has to be removed and then the flange hub, the pinion bearing adjustment is critical and unless you know exactly what to do and have the correct tools the differential bearings can destroy themselves if not set up correctly, the differential housing gasket requires the removal of the differential housing which means the axles have to be pulled out to release the differential, this means that the 4X4 hubs have to be disassembled to get the axles out.