My $0.02... I supplied a number of parts and noted that something pertaining to the valves was returned to me. I said, "they come in these little inch square boxes, Corteco brand. I just assumed that they weren't comfortable using parts supplied by me and used their own." His response: those are the Mercedes parts, they could have forgotten to do the valve seals. It's possible, people make mistakes."
Put off any focus on the bottom end (leak down test, additional compression tests, etc) because there was no issue before you had the head done and you have observed there is no appreciable crank case pressure indicating ring issues.
Spend your money this Friday having the mechanic remove the parts necessary to allow an inspection of the upper end of the valves, guides and seals to take place. First step would be to see if the seals are there. Second step would be to wiggle the valve in the guide to see if the guide is worn. Third, he should be able to measure the valve stem to see if it is worn. Finally, he if nothing else is found, he can install the new seals that the other mechanic returned to you. This is money better spent than leakdowns and compression checks on a motor that has no indication there is a bottom end issue.