old thread but i will add to it . When i replaced my mounts there was a lot of corrosion under one (your choice to look) , and i felt had of kept swinging on the mounting bolts i could of crushed the chassis in . my chassis feels solid , maybe im wrong and its rotten ? or you can crush the chassis even if its a new chassis ???? . i put spreader plates under the nuts . (big square washers) .
Doing it again i would of pushed the bolts out with a smaller bolt and left it in the hole , don't know if there is but i would guess there's tubes inside the chassis and perhaps they fell out of place and allowed the crush effect . THIS IS ALL GUESS WORK on my part , just my findings and best to ask first .