Today I noticed something strange. Had the engine on the workbench and decided to pull the clutch, measure the main shaft axial clearance, and eventually shim it out due to the unavailability of the 'graduated bearing retainer'. Well, axial clearance was way too much. It soon became clear why: the main bearing worked itself outwards. Huh, strange. That bearing is held in by a bearing retainer. Unscrewed the retainer, which displayed a nice groove where the bearing touches the retainer (top retainer in the image below). 'Well, let's see if there should be a groove of any kind. Let's check the retainer from the spare engine. Removing it is only a 5 min job'. Surprise: same damage but to a lesser extent (bottom retainer in the picture above). As far as I know only a spinning outer race of the main bearing can cause these grooves. Not good. 2 LC4 engines, one 2003, one 2005, same issue. Both with the roller bearings. Can't be a coincidence. The roller bearings seem fine in both engines; running surfaces are smooth and undamaged, and so are the rollers. There are marks visible on the rollers from axial loading, but they have no depth. Anyone seen this before? Is there a hidden problem somewhere? I used some acetone to clean the area as well as possible, applied some Loctite 603 retaining compound (capillary action draws it between bearing and casing), and tapped the main bearing in until it was flush with the casing. Have to order a new retainer, though.