I wouldn’t mind betting that you will be the first to the groundbreaking attempt Jim. Not a lot of room twixt tub and bottom plate to get the weight into position. The manual says tub out of cabinet and I’m inclined to think that the only way.
I have known a couple engineers that have managed to squeeze the balance weight in from the bottom, only problem is the new balance weight came loose and a new drum was required, thats the main failure on the Aqualtis is the balance weight coming loose, the 1st ones had a shakeproof washer on all the bolts and none of them seem to come loose, so unless you loctite the buggers in you will be back i’m afraid.
The bolts were actually quite tight when I removed them on Monday, the weight wasn’t ‘loose’, it had broken apart. I just leant it back, dropped the pump down but left it fully connected and it took less than five minutes to slot the weight in and refit the bolts, did stick some loctite on them to be sure. 8)