I like Sierra. ....sounds like heresy as a past Merc disciple.
I've never had a problem with their Merc parts, including carb kits. I've used their Alpha II lower unit seal kits, shim kits, prop shaft pinion needle bearings and gimbal bearings (same Torrington and Link Belt parts). Also Sierra prop shafts, engine coupler yokes, drive gear yokes, and lower pinion drive shafts.
I worked as a drive train mfg engineer before retirement, and I have a .0005" digital mic to prove it. Their parts measured up to OEM measurements and friction welding stds on the wet/lubed shafts. ...I always figured they sourced from Merc's source on these.
I had to replace a FWD gear set after a wing dam pile up. I went with Merc OEM. Spiral gear sets and their shimming tolerances have zero room for error.