Hi Peter
What an interesting story.
You can find details of the RM's on Leviathan at Trafalgar in 2 ways.
Firstly all the original muster books for the Trafalgar ships are in the National Archive. So if you can get to Kew you can see George Wingrove's entry in the original Leviathan muster - plus you can get details of all the other RM's.
Alternatively you can get the information from the Ayshford Trafalgar Roll. This is a CD which was produced/sold several years ago. It contains a database of all the muster entries (plus other info) for all the ships at Trafalgar. So you can easily search for all the RM's on Leviathan and it will produce a user-friendly list in the blink of an eye.
I would willingly do the latter for you - except for one problem. I just looked for my copy of the CD and I can't for the life of me see what I have done with it. The nightmare will be if it has got caught up in a file. If so it might not see the light of day for some while

So if anyone else has a copy of the ATR maybe they could help Peter out.
All the best and good luck with your research.
Mark Barrett