I hav'nt tried 2mm hex key, but i think i've figured it out!
The bass was purchased in second hand condition and to be honest i don't think the previous owner gave much care towards it as there are quite a few scratches over the body/neck which you'd probably expect from a well gigged bass? But from the description i was given from the seller it was only ever bought out for special gigs! so i believe a few little porky's were told to me. Anyway i think that they tried to adjust the saddles with the wrong tool and ruined the hex slots on the grub screws, which isn't a massive headache as i can buy some replacements but the fact that i was deceived in the description has pissed me off.
So in future when buying a used bass i will try and try before buying!! lesson learned.