Hi Froggee. The L class versions on the DLS are indeed legacy content as you know, but after examining them in CMP, the errors that mostly show up for them are simply the old 'Progressive Meshes are no longer supported yadda yadda yadda," and a problem with a shadow texture. From what I'm aware, there is a reasonably straightforward way to convert old style .PM meshes to the modern .IM mesh used by modern versions of Trainz, which would eliminate those annoying errors. I can't remember the exact details though, but I'm pretty sure there are guides found elsewhere on these forums which detail how to do it.
As for the shadow error, if I remember rightly, the way to fix that is to open the file for edit, then open it's Config file, and delete the entry for the shadow texture and recommit it (it's wise to back up the config file first before making any alterations of course). However, I'm not 100% sure, so it would be best to wait and ask for clarification first from someone more experienced in fixing these errors before doing this, as I only have minimal experience fixing faulty content.
It should also go without saying that if you had 2010, all the L class units available do in fact work with 2010 under Compatibility Mode (which is what I use as a stop gap measure). However, as you don't seem to own that version that's not an option for you sadly.
Thanks mate, i will look into it