It is ready for an oil change (first since I bought the car) so I put some Seafoam in the crankcase. I read that this generation Avalon is subject to oil sludge if oil changes are neglected. I have no service records on the car, but it runs great. Anybody had oil sludge issues? Anybody use Seafoam in their crank and, if so, does it help? After 170 miles, the oil looks darker on the dipstick so it seems to be doing something. Thanks.