Hi,
The 105 is in .177 calibre and the 106 is in .22. The earlier versions had the two open rings to the cocking arm as in the advertised example and sported a better rear sight than the later version.
The pistol looks in good condition and can quite easily be resealed should there be any air leaking issues. As stated in earlier posts, with care and limiting pumps to around five or six you shouldn't have too many problems.
I would say the advertised pistol is at the high end of the price range, but given how how rarely they appear on the UK market, I would think the price worth paying to acquire an early example.
Hope this helps
Brian