I had that trouble with an old set of headlights once try basing down on top of the nipple bit I had to do that to get it come back on
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Colorado Red 07 Plate ST
Mountune CAIS - 60mm Throttle Body - Full Resonated Milltek System - Bilstein B12's - 300mm front discs - Gloss Black Team Dynamics Pro Race 3's - Tints - Red-Black DMB Badges and loads of eBay stuff...