After several months of trying to locate a resonating noise coming from the rear of my 40 wagon at 40mhr. I believe I have finally isolated the problem this afternoon.
Traveling at around 60 the car suddenly shuttered,losing power momentarily, followed by a grinding sound coming from the rear axle.
My first thought was that I had blown a wheel bearing. After nursing it home I discovered what appeared to be gear oil blowing out of the top vent,leaving a small puddle under the axle gear housing.There was no oil leaking out the wheels.
In recent weeks I've also noticed that when I take off with a slightly heavy foot,a momentary oscillation in the torque that occured up to 15mph. I attributed this to the slight play I noticed in the transmission bushing and mount. Now I'm thinking that the carriers are the problem. I imagine that I will have to take of the back cover to check the axle.

I'm also wondering if the car is worth repairing. The body is sound and has 186'000 miles. The only significant rust other than a few patched surface spots was on the bottom edges of the drivers door that I repaired. I also had to weld in a 18inch section of the inner and outer sill a few inches into the floor pan under the front section of the drivers door. This was taken from a rust free 240. Concerned about the cars structural integrity .I welded all the seams. This wasn't tack welded. I have supported it there with the jack stands and it looks as good as it did when I completed the job 3yrs ago.
The motor runs great but I'm smelling antifreeze once in awhile when accelerating and am leaking oil on the right side of the block which could be coming from the head gasket. The suspension is tight. Front dust pans, wheel bearing, rotors,calipers and the cat converter on back was replaced last year and basically rust free.
I have a 91 wagon that is rust free but will eventually need a new tranny. I guess the bottom line is if the axle is shot, whether to repair or salvage the parts .