Rubber piece thats on the left part of the head is leaking coolant. what is it?

[RNEMESiS42]

I was up north near Lake Superior, far away from home. This is where I purchased my Supra. I drove it back on the highway the night I bought it and all of a sudden after 20 minutes my temp started skyrocketing! I pulled over and opened up the hood. I feared a BHG...that must be why that old dude sold me his Supra with so little miles on it. Turns out that damn random ass plug was spewing coolant out my engine. I drove the car to a rest stop and ended up hitch hiking back with some nice/crazy Christian dude to the cities.
The next morning I drove back up with a buddy with some random small hosing and clamps from autozone. I got that all on nice and tight and haven't had a problem with it since. Really, did they just put that shitty piece of rubber there to make life miserable?
I probably should "offiicially" replace it sometime, but it hasn't leaked in four years.