I have an 81 300sd with 334,000 on it. Have changed the flex plates and recently had the driver's side rear wheel bearing looked at because i was experiencing a clunk when i put the car in reverse. The mechanic said the bearing was going, but tightened it up and now the clunk is better ( a temp. fix... part is on the way...) but i have been noticing a 2 stage clunk when i accelerate after the car warms up. if i depress the accelerator quickly and let up quickly it clunks on the depression and release, also when the tranny downshifts when there is no load on the drive line, like when i am coming to a stop going up hill. any clues? i have noticed a slight leak from the pinion seal and have examined the driveline quite a bit. it rotates a tad in park, and makes that familiar sound if i grab it and give it a quick hard twist ( moves about a quater inch in rotation) could there be slack somewhere in the tranny or drive line or differential?!?!? the u-joints seem to be tight.... help!