It's certainly worth diagnosing but it won't cost $500! First off, with coolant dripping on the cap, not replacing at least the cap and rotor is asking for problems. A cap and rotor kit runs about $145. If you don't spend money on that but buy the entire distributor you're out $379.

With a situation described by the original poster, I'd still replace the whole thing if I was in there...working outside in cold temperatures with limited time available. But that's just me......