I have a 94 E420 that I bought with spark issues. I replaced a cracked cap and cleaned the other in my driveway in January. It's been sitting since and I've been trying to start it weekly to keep it in running shape until they stop salting the roads. However I neglected to do that for a little over 2 weeks and now the caps are full of moisture again and it had a hot start issue.

What's the permanent solution to this? I replaced one with a Bosch part I purchased new and it had this issue still. I'm rather disappointed in that.