Bottom pulley alignment

This car is trying to bankrupt me... it's a 2001 1.8T vRS.

Had the RAC out to jumpstart me the other day after my dash lights started appearing - pulled in, knocked it off, wouldn't fire, diagnosed flat battery.

Fair play thinks I, it's done 175k and even if it's the second battery its still not bad. Obviously wasn't charging, so fitted new alt and new battery together. Took it for a test, was fine but charging light flickered at idle. On closer inspection, as soon as I was firing up the engine the belt was slipping 1/8th of an inch to the drivers side. Looked at the tensioner, clearly worn to an angle - ordered a new tensioner from Jorily (Ta muchly, if you're reading) - and fitted a new belt as well.

All back together, belt still slips by that fraction - the bottom pulley (crankshaft) looks like it's pushed itself out by enough to be pulling the belt to the side.

Anyone experienced this before? Does the crank pulley have a rubber damper on it that may have come adrift? Apart from this, the car idles and revs perfectly, no mechanical sounds to make me think anything's wrong in the crankshaft area... going to investigate it tomorrow, just wondered if anyone's seen it before.