Sometimes, the retaining clip that holds the GP style buffers in place can rot out resulting in them being drilled out to accept bolt-in ser3 buffers, which can be a tricky job to get them spot on in the right place. (it usually results in ovalated holes

). If you remove the buffers and inspect internally you can usually see remnant traces of the old clip if this is the case.
Unlike early Ser2 forks, Ser3 forks have one of the 2 buffer bolts on each fork boot sitting in a recessed part of the seam for the bolt head. This recess isn't there on GP fork boots further supporting that they have likely been drilled out.
Alternatively............ maybe someone has grafted a Ser3 fork tube onto a GP fork stem? (check the welds here)
