Pretty rare......
For WMMT3/DX+ try looking for the manual for WMMT2 (or 1). The few times I opened up my WMMT3/DX+, it's appeared to have been an upgrade from an earlier version. I say that because, it has the chihiro power harness not connected.
As for WMMT4, seen a couple of mobo's on auctions, buy scared to pull the trigger. I suspect the service screen is in japanese, and don't really know if namco/bandia changed the JVS or servo board