Rubber sealant on top of heater box?

[Vref]

Anyone know what a good sealant to use is on the top of the heater blower box on the firewall so it doesnt leak? I can see a small visible gap under the plenum (despite brand new gaskets) and it will definitely leak if not fixed. I'm sure the original stuff is no longer available. The NCRS manual says its a rubber sealant. Thanks

 

[I_R_DA_ONE]

Go to an electrical supply store and get some raw rubber tape [Scotch or 3M brand] It comes in a roll...it is used for high voltage wire sealent and it is very close to the orignal sealent....this tape will form to fit most all the uneven openings that you may have....

Mike