CaDLoN

Hi, Newbie after some advice I've owned for the about 8 years a Weihrauch HW80 with a Nikko Stirling 6x40 Its been sat in the cupboard for the last 2 years, i seem to recall it had quite a twang when fired. I'd like to get it overhaulled, make sure its running to correct spec, make sure its not under and definatly not over powered I dont mind having a go my self, but preferabley get it looked at by someone reputable/professional, does anyone have any sugestions? Thanks in advance