RTV is used on joints, irregularities and damaged sealing surfaces. Spray Coppercoat is a good light sealer for most gaskets if allowed to dry before assembly. Factory gaskets should always be used UNLESS a design change in the assembly warrents a specialty gasket. As Robbie pointed out, a thin application of weatherstrip adheasive is an industry standard trick of securing difficult gaskets (one side only!) so hands can be free to manuver pans/covers into place. Consumer RTV use has probably made more shop owners/mechanics mortgage payments than any other over the counter material!
Cork gaskets are excellant especially when the manufactures started adding bits of neoprene in the compound. The biggest reason for failure is overtightening. When assembling ANYTHING, a criss cross pattern should be employed so even pressure is applied. Never tighten one bolt then another but rather continuous snugging followed by final tightning. In the case of cork or neoprene only tighten until slight bulging happens. Never tighten to the point of a "tight" bolt! Use of "slick" sealants on cork or neoprene (rtv, grease, oil, wet Coppercoat) will encouage the gasket to squish and fail. RTV (silly putty) being a liquid will not compress and will deflect out from between the sealing surfaces. If you see the RTV bead outside then you can bet the same amount is squeezed inside! As pointed out, you do want a dab of RTV wherever gaskets mate, crossing other gasketed area's and sharp corners.
O-rings and flat gaskets should always be torqued to spec as they are usually found on aluminum accesories. A light spray of Coppercoat on flat gaskets will insure sealing without weepage. (Again, let the Coppercoat dry before assembly or it will stick and be a PITA to clean off later!) Aviation sealer will seal well on damaged flat gaskets but is a major PITA to get off! A light coat of oil on an O-ring will ensure it comes out next time the part is removed. If the o-ring is prone to slipping out of position before it gets sandwiched some white lithium lube will usually keep it in place long enough. Never use moly based lubes on o-rings as it can attack natural rubber that o-rings are often made of!
If a flange type of seal is needed and a gasket in unavailable use a flange sealant instead of RTV! Flange sealants are designed to be put on very thin and even and they are resistant to flaking off at the edges incase of over application. Anti-seeze should also be used on torqued bolts and any steel bolt threaded into aluminum!
Hope that helps! Sorry if my professional factory training let anyone down!
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