I'm trying to restore a 10-speed Dawes from the 70's. The pulleys on the rear derailleur-A Simplex Prestige (red badge)-are completely worn. I'm wondering whether it makes sense to just replace the pulleys (from what I've seen online Sun Tour pulleys are compatible with these), find a Simplex Prestige online or get a new derailleur altogether. From what I've read, the derailleur I have is not the most long-lasting, with the plastic parts and all. Mostly what I'm asking is how do you know what parts are compatible?