Coolant leak from block heater hole

[Billdozer2]

Hey guys, I've had a really small coolant leak coming from where the block heater goes on the passenger side of the engine for awhile. It only leaks when it gets real cold out. During the summer months, it's completely dry. BTW, I have a 2250 in a 2013 Volvo. I do not have a block heater installed. There is just a small plate there. I've heard from a couple different mechanics that this leak is pretty common and they have told me that if I go ahead and replace the o-ring, there is a good chance that it will continue to leak anyways. Has anyone else seen this and what have you done about it? Has anyone replaced the o-ring and had good results?