If you're looking to buy a used Marshall 412 cabinet and it appears to be "Well used", then before you buy it you should take the back off and then check the cabinet for solidity and rigidity by pushing on the back corners. It'd be an even better test to remove the baffle as well, which would remove all bracing support from the cabinet, but you can tell if the cabinet sides are still securely glued just by taking the back off. I got a 1960B cabinet recently, a well used one, and when I went to recover it, I found a high water mark in the cabinet about three inches up, and when I removed the back and the front baffle I found that it was a bit wobbly. After removing the tolex it was soon evident that the glue joints had all completely failed. The old glue was crumbly grit like coarse sand. It was no effort to completely disasemble the cabinet. I brushed out all the old glue with a stiff brush and glued it back together using the baffle and back as internal braces and used every long clamp I had available (Just enough fortunately) to get it clamped across every joint. I suspect that a lot of old Marshall cabinets have suffered the same glue joint failures. But you can't really tell when the cabinet is fully assembled. It's being held together by the baffle, the back, and the tolex. My cabinet in question was made in the mid 80s. It's a JCM800 era 1960B.