All but the late 08 & 09 bikes had those as 5mm allen. For some reason they went with torx (T-25 or maybe T-30) on the last two years of production. They should not be that tight as the o-ring does all the sealing once you snug them up.
Thanks John! Mine is a '09 model and apparently has the Torx screws. I was confused by the maintenance video I purchased which suggested these were 5mm Allen screws. I'm sure the video predates the '08 model and I wasn't aware of the change. The Torx drivers I have don't seem to fit well and I didn't want to risk stripping the head.
The Torx system has a few obscure sizes within the range. E.G. there is a T27 which (of course) sits between the T25 and T30, but many sets of the keys don't contain that size. It may well be your answer the loose fit. If you can get them out it may be easier to replace with M6 screws (5 mm Allen key).
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