2001 Ford Ranger 4.0L SOHC with 150k miles I replaced the thermostat & o-ring at 145k miles. It's been leaking since. Took it apart & saw that the upper thermostat housing was buggered up on the sealing surface. Installed a new Ford Motorcraft part (only $10 and made in Great Brittain!). Still leaks between the upper & lower thermostat housing. Took it back apart & the o-ring (Fel-Pro p/n 35617) doesn't fit tight around the thermostat, but I don't think it's supposed to as the housing does the sealing. Is that right? Also, o-ring looks a little flat but I torqued the 3 bolts to 89 in-lb per the factory service manual. Is there a trick that I'm missing? I've got another o-ring, but I wanted to check in to see if I'm not doing something correctly before installing & putting back together. Thank you.