If you lay under the truck in front of the rear end were the drive shaft hooks up to it, on the left side of the housing there will be a plug. It may be covered with dirt or grease , clean , and then remove it. put gear oil in there.
read the manual
The rear differential fluid goes directly into the rear differential. There is normally an inset plug that has a square drive on it that accepts a 3/8" ratchet or ratchet extension. Remove this plug. If fluid comes out, you do not need to add any. If no fluid comes out, add enough of the fluid recommended by your vehicle manufacturer (normally 80/90 gear lube, but not always) where you took out the plug, until it starts to seep out the plug hole. Replace the plug and you're finished.
Look at the rear differential housing - you will see two plugs in the housing an upper and a lower. Loosen the upper plug - if fluid runs out of it you have sufficient fluid - if not - add fluid until it just starts running out - then replace plug.
The rear differential is a part of the power train, not a part of the suspension on a vehicle. It is the suspension system you need to be investigating on your vehicle. You more than likely have a broken spring.
To change differential fluid on a 1997 CR-V the vehicle needs to be lifted up to reach the rear differential. Find the drain plug located on the underside of the unit. Pull the plug and drain the fluid, when done place the plug back add fluid into the fill hole which is located topside of the differential.
On the upper right (passenger for a left hand drive vehicle) side of the differential, there's a plug. IIRC, you need a 3/8" drive ratchet to remove it. That's where you add your diff fluid.
go to a GM dealer and they have a limited slip additive that you add to your rear end fluid.
In a 1997 Ford Aerostar ( REAR differential ) With the 7.5 " ring gear ( 3.5 U.S. pints ) With the 8.8 " ring gear ( 5.0 ) * traction lok , add 4 ounces of friction modifier
Assumeing you are at the rear of your van, if you crawl under the rear bumper you will see the rear axil, the center of that axil in the differential(round part)you should see a bolt or (plug) towards the top left side facing fprward the vehical this is where you can add differential fluid you want to fill it just below the leval of the hole.....
When the fluid falls below the bottom of the filler plug hole it is time to add fluid. Add fluid until the level reaches the bottom of the filler plug hole. In other words, add fluid(while parked on a level surface)until it begins to run out. I have a 99 Tahoe and the manual doesn't list any quantity/capacity for the differential, only how to check the level and refill if needed. Mike
Get a lube shop to do it.
Through the dip-stick tub. Do not overfill.