I just registered and this looked to be the right place for this, but if not, moderators feel free to move it.
I have a 2000 Toyota 4Runner that has been taken care of and had no major mechanical problems up until a week ago when the rear differential started leaking. Long story short, I drove about three hours on the Interstate like that before I started to hear a high-pitched whine as I pressed the accelerator and realized something was wrong. By the time I got to it the differential had bled pretty much dry. Rusted through near where the e-brake cable is supported. I refilled it, of course - it took over three quarts.
I still hear some funky sounds when I'm driving, though not as severe. Mostly it's just a low whirring sound as I'm coasting or slowing down. So, obviously, this needs to be fixed. I'd like to do it myself if I can, without half-assing it. First I'm going to clean the vent on the differential because I'm sure it's plugged. Also I expect the differential is filled with a soup of oil and sheared metal, so I'm going to drain the oil (just topped it off before) and between an air compressor and a magnet I hope to be able to remove all the loose filings - hopefully that is what's causing the noise I hear. I'll have to remove all that rust on the case, though I'm not too eager to bring any power tools near the thing, so between Naval Jelly and steel wool I think I'll be able to clean it up. Some solvent will be used to ensure all the Naval Jelly and oil is off the metal before attempting to repair it. After that I plan to patch it with either a gas tank repair kit or some steel filler epoxy that I've seen advertised for repairing oil pans (leaning towards the steel epoxy, as I expect it will be easier to sand and paint). Then I'll fill it up again and hope it doesn't fall apart.
Does it sound like I'm headed in the right direction, or should I just take this thing to a mechanic and expect to pay $2,000 for a new rear end? What I'm most worried about is if I try to repair it on my own and upon removing the rust I find that there's nothing left to patch beneath it.
One other observation: Starting a couple days ago I noticed that the shifter doesn't seem to find the slots as well as it used to. It's an automatic. I first noticed it when I put it in park and went to take the key out, but couldn't. I touched the shifter and it clicked into park although I thought I had already set it there. Since then it's happened a handful of times (in any gear/reverse/neutral). The shifter doesn't take any force to move it or anything, it just doesn't seem to click into place as neatly as it used to, and I find myself having to wiggle it occasionally to make sure it's "in" the place I set it in. That's sort of an obscure symptom and I'm not sure if it's related, but I thought it was worth noting.
Thanks in advance for any advice.