Frost Plug Coolant Leak?

[82DMC12]

Group,

This is the other issue I'd like to get fixed on my car, in addition to the PCV valve post below.

Again, i have a 1994 ES300. The same day i replaced the PCV valve I noticed that my coolant reservior was a little low. I check all fluids frequently so this was odd to me. I found a small streak of coolant on the front frame which I found to be sourced at the frost plug looking thing just to the left of the oil filter. it is a plate held to the head with two nuts. I am pretty sure this is where the leak is coming from - I blew out the little lip below it with shop air and ran the engine for a while - after about 15 min i finally saw a little fluid seeping onto the lip. There is no other place for coolant to be coming from because there are no stains or fluid leaks higher than this lip. ... well unless the head had a crack in it which i doubt.

I had an independant mechanic give me his opinion and he agreed with my conclusion. I ordered a new plate from Lexus and the tech told me to seal it with black RTV. is this a problem anyone else has seen? what is the function of this plate? I don't see how the plug could pop out if it is held in place with nuts, unlike a traditional frost plug. the dealer told me a block heater is usually put in the plug by the firewall.

Any tips on replacing this thing? Luckily i have all the right universals and such!

Thanks,

Andy

[SKperformance]

My block heater is to the left of my filter if looking at it.

So the non option plate is their instead.