A couple of things you need to do. First, delete your other thread, no need for two threads as it will only get confusing for everyone. Second, take picture of the ID tag. Product Identification number (serial number) is located on the right side of the rear frame. We need this number because there were two different decks used on the L120. Third, when was the last time you replaced the deck belt? Fourth, Have you checked all the pulleys on the deck for wear. When you answer these questions we will be able to provide you with help.
#3
tom3
I double check the tensioner. That is a one belt deck (?) with a really long belt. That tensioner can get dirty and won't keep up with the belt flapping around. Maybe time for a new belt too?