Hi Guys,
Just a quick update, I talked with my Triumph dealer this morning and confirmed that the arms are the same as long as you get one from the same model range, e.g pre 96 single headlight and post 96 with split headlight. I also found out that a new arm would cost £650 ukp

Got one off of Ebay for £47 incl P&P
Anyway, I hope this info helps.
David.