Here's my fix.... maybe after this I'll make a thread about call tuning...
I too had an original ol yeller, I love that slate... then it broke, Bought another and it too(like yours) sounding very hollow in the woods... so I tuned it up...
When I tuned this slate, I rolled up some rubber electrical tape and shoved it in the holes, then put tape over it to hold the new rubber posts against the sound board.
It may take a few to get it right, Here's a new Yella Hammer that would make Harold Knight gasp....