I have a 2016 4Runner Trail with approx. 140k miles. The driver's side parking brake shoes and drum have differential fluid on them. The vehicle sees 90+% city and highway driving. I've done some occasional light off-roading (no mud) and occasional towing of a 2,800 lb trailer. No accidents.

From my internet research it looks like the differential fluid leak would be coming from the seal in the axle housing. What could cause that seal to fail at this mileage? For reference, I also have a 2006 4Runnner Sport with 196K miles and zero leaks from the original rear axle seals. That's why I'm surprised to have the leak in my 2016 with only 140k miles.

Do I need to replace the wheel bearing assembly in addition to the axle housing seal or can I just replace the axle housing seal? No slop or play in the wheel bearings and no noise.

I discovered the differential fluid leak at the driver's side parking brake when I went to replace the rear pads and rotors a couple of weeks ago. Passenger side parking brake is clean and dry as it should be.

TIA

sh1t happens. does suck tho. should just be a seal job. "just"

thanks for the reply. that's what I'm hoping. I know the rear wheel bearing replacement requires a press, special tool(s) etc. so I'm hoping I can address this with just a seal replacement rather than seals and wheel bearings.

not sure if my info was 100% correct, so here is a thread/couple videos. I didnt watch them Rear Axle Seal / Bearing Replacement

Thanks for those links! I've watched those videos and a few others. I am on the fence about whether or not I actually need to replace the bearings or just the seal in the housing.

As of this post, my plan is to pull the axles and visually inspect the seals at the wheel bearing. If those look good, I will only replace the seal in the housing and just leave the wheel bearings alone.

Edit to add: I just double-checked the wheel bearings for play/slop and there is none on either side. They are smooth, solid, and quiet.

One other thing you need to check is the diff "breather", if it's clogged it can allow pressure too build up in the diff and force lube pass the seals, it's most likely isn't the issue because both seals might leak because of the pressure but it still could be only one seal if it's more worn than the other.

@AuSeeker -

Thanks for the suggestion. I checked the axle breather. The metal cap was a little crusty, but not badly rusted or corroded. I spun it back and forth several times to loosen it up just to be sure.