I retired an '88 Cougar w/3.8 at 300K miles that I purchased brand new. (This car didn't have any head gasket problems) The engine was still good, but everything else on the car was nickel-and-dimeing me to death. I pulled the engine on it and there were no deposits whatsoever. The inside of the valve covers were spotless and there wasn't even any deposits in the oil pan sump or lifter valley. I did change the pvc valve quite often, but nothing was ever changed internally and it was a very reliable car. While I drove this car, I never had an oil pan or valve covers off.
I was a little meticulous about oil changes back then and I changed it about every 2K or 2.5K miles. I also used about every name-brand oil under the sun and it was probably a different brand every time. I also used mostly cheap Fram or Motorcraft filters, but I remember quite a few other brands on there also.