Some of the riser gaskets are supposed to not have sealer on them. But the thermostat gaskets and bolts at least on OMCs (and many Volvos used the same thermo housing) are supposed to get OMC gasket sealer (OMC gasket sealer is supposedly the same as Permatex Aviation Sealer). I have used this stuff every time I have changed a thermostat (and that's about once every 2 seasons because they get sticky in salt water) and they never leak and the bolts always come out. The sealer keeps moisture out of the threads and prevents corrosion. Works well on any bolts on the outdrive that are in salt water the whole season.
If the manufacturer says not to use on riser gaskets, I would probably not, but I might still put it on the threads of the bolts, because I have had great luck doing this on all my fasteners on the drive, water pump, etc.
_________________ 88 Four Winns 200 Horizon 4.3 OMC Cobra-4bbl 2002 Walker Bay 10/2012 Suzuki 2.5 2008 Walker Bay 8
1998 Jeep Grand Cherokee 4.0/Selectrac 2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II
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