I've got the exact same bike as you and my BB started creaking and I could feel the bearings weren't right. I was told by my bike shop (Really good Giant suppliers in Clapham) that I could only replace my BB with the mega Exo (which I got after calling various local bike shops). I was also looking at other BB's, as the reviews and my own experience of it (mega Exo) wasn't that good. I had only completed about 6000 miles all in all weathers.
One bit of advice I was given was that the pressure washers that are used for cleaning the bike can push the grease in the bottom bracket out, which leads to further wear.
- Have you tried opening it up (you need the tools) and tried cleaning and re-greasing it? If not a new one is likely to set you back £40-50.
I'm a little bit skeptical about the guys in Clapham who told you that you'd have to replace with another MegaExo. I really want to go for something different, and based on the dimensions of my BB, I reckon I should be able to replace it with another UK standard BB?
Or is it that I need to replace the whole chainset along with the BB in order to use a different one?