2000 Camry LE 5S-FE engine, automatic transmission, and 182k miles. When I got the car, the differential drain plug was filled with black sludge and tiny metal needles; the differential fluid was black, so I kept changing it (drain and fill and NOT power flushing) after driving for a while until it stayed pink. I fill it up only with Valvoline synthetic ATF. I've also been removing the drain plug and cleaning it ever since, about every 100-700 miles. This morning, I just checked it after cleaning it 34 miles ago and the drain plug was filled with black sludge (the fluid remained pink). The only unusual thing happening is that the car ticks/rattles in first gear, but not in other gears.

What does this sludge and how often should I be cleaning the plug?

Thanks

 

Normally one only cleans the plug when its time to change the oil due to miles or years.

Make sure the vent for the diff is clear. Vent is on top of diff.

Could fill the diff with kerosene or diesel then drive car back and forth in driveway a few time then drain. When done cleaning then flush out the solvent with ATF.

Try to determine if the clicking/rattle is trans/diff or axle CV joints. For CV joints make a few sharp left and right hand 360 turns at low speed. Listen of clicking or popping noises.

 

Thanks.

Looking down at the diff, I can't see that vent.

The noise is when I'm driving straight, not turning.