The O-rings on your Sinclair bore guides, snouts for Sinclair All Purpose Rod Guides, Solvent Ports and Chamber Plugs should be replaced occasionally because solvents and use eventually wear them out. We use three sizes of O-rings only, so having some spares on hand is not expensive. The 222 and 223 family of guides and the 17 caliber guides do require the O-ring installation tool included in the O-ring kits. The two larger size O-rings can be installed fairly easily without the tool, though the kits include the tool for almost no additional charge over the 10 O-rings. All three O-ring sizes are available separately in 5-packs.
Sinclair, Issue:4A, Page:140