If I were you, I'd head over to Pensbury Manor
, Syd Saperstein's Wahl-Eversharp site. He's probably the top authority on these pens, and by looking around you can probably ID the pen. Drop him a line with questions about getting a nib, etc.
As a complete coincidence, I had a great chat with him on Friday afternoon at the LA Pen Show. Learned a boatload of stuff about the company's history, and all the pens, and saw all their newly-introduced pens - the are *fabulous*! One thing he mentioned was phlorescence (not sure of the spelling) which would occur with some of the W-E plastics. They become more transparent and almost seem to glow... when the plastic is starting to break down. The top of the cap on your pen may be exhibiting that, so just handle with care.
Best of luck - I saw a LOT of beautiful W-E pens at the show, not in my pen budget for this trip, however...