I've replaced my seals already. It is a lot of work, but it can be done. But someone mentioned compression, so check that too because piston rings are like valve seals, they wear out and allow oil to pass through them. I had to place both tnings on my engine and yes did it myself. Its a lot of work and time consuming task, dont expect to finish replacing the valve seals in one day if your a novice.
1992 Crown Victoria LX 150K AOD 3.08gears
-A/C delete (w/ condenser & accumulator), -CVPI Aluminum Driveshaft, -Cold Air Intake, -Electric Fan, -'96+ Intake System, -180� Thermostat, -NGK Iridium Spark Plugs, -FlowMaster 40 muffler, -UnderDrive Pulleys (excluding WP pulley), -Battery in Trunk