No, have not had any problems with mine.
I'm assuming yours has corroded from sitting with water in it?
 
My first step is usually INOX when things are stuck, but in this case im not sure what this would mean for your seals.
HMMM? hope you find a solution D.

try filling the heater core with soluble oil it works its way out the tap worked for me. I have always been able to replace the o ring seals in the tap when they start leaking. Most expensive problem is replacing the core not cheap to have one made!!  I usually leave my heater turned on and just turn off the airflow through it

In all my heater units, the heater tap is very tight and borders on seized solid, hence the welded tab you have D.

I have pulled mine apart a few times and soaked the O-rings in molycoat 111 (oxygen friendly o-ring grease). If the O-rings are saveable, then molycoat will do it.

As for replacing the heater core, I took mine to a radiator place, and they re-cored it for me. its just a mini radiator after all. It was a while back, but I don't recall it costing a fortune.

I use good old castrol soluble oil run it for a couple of days if you leave it to long can tend to soften the hoses. I agree with dundee leave the heater tap on the flaps do control the heat. my last heater core cost me $140.00 and agree they are only a  mini radiator but if they don't stock them ( no one does lol) as soon as they say modify one to suit mate you pay big time.