With 2 different metals in seawater you have the setup of a battery, right? The 2 poles of a battery. If you bond them, then and only then a current may flow. So don't bond.
BTW, the teflon tape will not entirely isolate the 2 parts, so they are bonded. Perhaps 6 months ago you went the cheap way and bought the pipe at a plumber shop and got some brass alloy which is not marine brass or bronze. So get an elbow of the same alloy as the strainer body or get a Marelon type as Brian suggested.
Oh, and the reason why it is recommended to bond everything (again, only if identical metal) to the ships ground system is to have it grounded for other purposes, like lightning ground.

Best regards, Wolfgang