Coolant Loss

I have posted on this vehicle before and gave a complete rundown on what I have done to find the leak. Found bad Intake gasket and replaced. Fluid loss continued but was less than before replacement. The vehicle is not driven much at all until recently. My grandson lives out of state and comes back every two weeks. For the past three months I have lent him use my truck for about eight days at a time and he drove it hard in town and freeway. For the past three weeks I have not had to add any fluid, the leakage seems to have stopped. Checked it again this morning and no fluid loss! Any ideas on what could have caused this change? I was going to pull heads and have them checked but now I don't know. There have been no SRS lights since changing intake gasket and knock sensors and fuel trims look good. I am totally confused.