Please help
 

https://cimg0.ibsrv.net/gimg/www.rx7...3553b30bce.png
1985 GS. This part of my rad is leaking like crazy.

Can someone explain it's purpose and if I can seal it permanently.

That's your Coolant Level Sensor. It operates by checking for electrical conductivity to ground that the coolant provides. If the coolant runs low, and the radiator isn't topped off, that sensor will be dry inside the radiator and the dash light will come on. You can plug it, but you better be in the habit of checking your Coolant and overflow levels religiously - or you're just asking for problems with overheating, and rotary engines don't do well with excessive heat.

If it's leaking, replace the rubber washer. If it's still leaking, check the bung to see if it's cracked. It has an important purpose, so be smart about how you handle it,

If it just needs a new gasket and you determine the sensor and rad are ok, order a replacement gasket from your local Mazda dealer. They will have it in a day or two. Also be careful it is plastic male threads and just needs to be snugged down.
OEM Part #:

8553-15-611

Also, is that screenshot an FC Rx7? Same sensor gasket on FC anyway...

Get your manuals here for your FB:

Foxed.ca