On my manual 124 the gaiter is held in place by simply stretching and snugging around a plastic lip or flange around the shift opening -- it looks to me like yours may be in place already...

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W108M117(1972) repaired after deer hit
W124M103(1987)
W124M103(1989) -- sold to son's friend
W124M119(1993) --
W124M103(1987 -- 5 speed Euro) - sold to forum member
W124M103(1989) -- TE
W123OM616(1977)
W201M103(1990) parts car