Try pulling the tranny oil fill plug and inserting air in the plug hole . If you hear hissing or such from the oil fill hole it's time for new rings , at least , no matter the mileage , as you have no idea what that motor went through prior .
On the same note , did you have the exhaust header and the intake disconnected when you blew air in the plug hole before ? If you didn't , you'd likely not hear anything .
And , of course , these tests should be done with the piston at TDC compression stroke . (edited)