Finally came across an MTH P5a without zinc pest! Saw one listed on the big auction site as a 20-5138-1, which wasn't one of the 2008 units (or any other other MTH product). The cab number (4703) matched the new 20-5738-1, so I figured it might have been a typo on the lister's part. I messaged them to confirm, and they replied that it was indeed a 20-5738-1. Managed to get it for around what that big Georgia forum sponsor tries to sell crumbling 2008 ones (with "cracked paint", as they list them) for...
Interesting note, the box it was shipped to me in had a tag on it from a previous recipient, Harry Hieke. Not this engine, as it hadn't been released yet when the tag was dated, but it seems the previous owner had sent an engine to Harry, and gotten it back (there was another tag dated later addressed to the owner).
