As I said before YOU HAVE TO replace both belts so that they will work together.
The whole set up is for them belts to work as a team. You replace one now you have one good belt and one wore out belt how can they work together. If you have to make the adjustment then you have other things going on as well.
My MTD is a 1990 just to name one of over 50 of them. And have never had to make the adjustment
(( racing is the only sport that you need two balls ))