Are you sure that the platter is spinning freely and not jamming so as to cause undue friction for the belt and pulley? Perhaps lubricate the spindle/bearing with some white lithium grease?
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You shouldn't be going through belts in 6 months. Try washing the belt with some dishwashing liquid to remove the oils and then treat it with some Aerospace 303, which should prolong the life of the rubber. The trick is to wipe the 303 off the belt until it is totally dry. This way, it won't slip. You should also wipe down the edge of the platter with isopropol alcohol to remove any oils that could cause slippage. If the belt slips after that, you'll definitely know it and you can just wash off the 303 with dishwashing liquid and start over or give it up and buy a DD table. Some people have substituted fishing line or some type of thread for the rubber belt, but I would try the 303 first.
If the belts are cracking, the last thing you should do is clean it with a solvent (alcohol). Cracking means that compounds in the belt are evaporating leaving it brittle.. you don't won't to remove more of what keeps the belt pliable with alcohol. You may want to do some reading on techniques used to preserve old rubber parts... might be that you need to keep 2 belts, 1 in a solution to restore pliability, the other in use and swap them periodically so as to recondition the one just used. Cleaning the belt with a soft cloth should be all you need unless you have an oops moment with Silclear or Cramolin. On the AR and Sota I have, belts never crack, they just eventually stretch too far after a few years.