rust in pulleys! 1979 300TD

[peachykeen]

the PO of my wagon left the car outside w/ the hood up to keep rodents from moving into the engine compartment for a couple yrs...apparently some rust started in the grooves of pulleys...after figuring out why my belts were prematurely dying...I sanded down as best I could inside the grooves...it has helped...now I can go about 1000k, but then the belts start getting whittled away...

any other suggestions OTHER than having to replace them? more sanding? i'm not confident taking all that apart -- so hopefully some other recommendations!

thanks as usual!