What dud shifters & what design Fubar? 105 is a brand name from Shimano, you really need to be specific to the model number, guessing if it's a Boardman and from eBay, it's 5700. What does early mean, could relate to shifters from the 1990's or 1980's by just saying 105 is to vague, as the 105 name first came out in 1985.

the 5700 series has been around long enough for any issue to become know with it, and if there are any, they are so minor, that they are not 'known' and the design is not 'fubar'

Would suggest contacting a LBS as your first point of call, as they can see/resolve any issues you have.