It is possible that the sealant clogged some passages in the radiator and now you have less cubic inches of radiator leading to less space for coolant to cool. There is always a risk of that when using those products. I have only used stop leak one time and I had good results but it was a new radiator that was bumped around pretty good in an accident. Other than some mist at one seam it was in good (almost new) condition.
What do you mean by maximum? Depending on your driving conditions (climate, load, traffic, etc it might be ok. If you are driving hard in a warm climate it might not get worse. If you are tooling around town on a cool day it may be much worse it he dead of summer.
I don't know if this helps ... you could have the radiator re-cored.
Rich
