Oil pooling on exhaust valve.

If they are J heads, the "valve seal" really is just a short umbrella that keeps most of, but not all, of the splashed oil from the springs off of the valve stem. There's always going to be some oil in the guides, if there weren't, the valves would seize up in the guides. I would ask the builder how much clearance they machined into the guides. More clearance, more oil.