You can do a leak down test with a cheap Harbor Freight leak down tester at about 7psi,to see if the head or base gasket,intake manifold could possibly be leaking by spraying with soapy water. If it's not holding the pressure and the gaskets,intake manifold,engine case halves,etc aren't seeping then it's probably the seals. Problem on the seals if you really want to test with soapy water,you have to pull the drive clutch,flywheel and stator to get to them and since you're already there,it's just as simple to pop them out and replace them anyway.