@Rickallan With a little bit of research (you can help to confirm my findings) you might find that this could be your solution.
Problem - Volume control pot not working and spins.
MXR-130 Service manual reported Supplier Part number VBV16-154BT4K7 (Look on page 26 of the copied version (Page 28 from the original printed version as shown at the bottom of the page) of the MXR-130 service manual for Item number VR452)
MXR-6250 Service manual reports the same Supplier Part number VBV16-154BT4K7 (Look on page 25 (31) of the MXR-6250 service manual for Item number VR902)
Looking for a volume pot for an MXR-130 did not come up with a solution BUT looking for a volume pot for an MXR-6250 came up with this,
CARVER 6250 RECEIVER PARTS volume balance board VR-764 with pots complete | eBay
The next step might be a visual confirmation that yours looks like what is pictured in the ebay offering. The 8 pin pot is for volume control.
Also, a question to the seller might be if the pot (the 8 pin pot) has a min and max stopping point and does not spin 360 degrees.
Best of luck.