This is on my 03 Lexus GX470
After noticing coolant level dropping in the reservoir tank, I went ahead and sent the oil for an oil analysis at 59k miles, they found Glycol in the oil
03 Lexus GX470, Valvoline Synpower 5W30, 59k miles - Bob Is The Oil Guy
Lexus dealer pressure tested the cooling system several times over 2 days and found nothing "abnormal".
My conclusion is it could be a small leak at the intake manifold gasket that does not show up during pressure testing. Is there any other way short of tearing out the intake manifold to confirm that?