I have a 1995 raw water cooler 350 mercruiser, took off thermostat housing p/n 16413-c1 stamped has no check balls. The thermostat sits on a lip within the housing has cork gasket then thermostat the plastic sleeve. Ok so after I pulled the housing off I notice the cork gasket was slipped out of the lip, upon further investigation I noticed that the LIP has an open where the water the water enters from the large hose, this is looking at the housing upside down, question is this normal? Why did the cork gasket slip out? The thermostat I changed last year!