Permatex® High-Temp Red RTV Silicone Gasket
OEM specified. Formulated for hi-temp applications, or heavy-duty use (such as towing, etc.). Replaces almost any cut gasket by making reliable “formed-in-place” gaskets that resist cracking, shrinking and migrating caused by thermal cycling. Coats pre-cut gaskets to increase reliability. Temperature range -65ºF to 650ºF (-54°C to 343°C) intermittent; resists auto and shop fluids. First generation 1970-1980 gasket maker.
Suggested Applications: Valve covers, oil pans, timing covers, water pumps, thermostat housings, transmission pans
It can be used to seal firesleeve but I would suggest thinning the RTV with acetone. Keep in mind this is not approved by the manufacturer.