I found that most of my oil leakage at teh 269,000 mile mark was getting out through the camshaft seals. Replaced during the front end 60K service, it also requires the removal of the two camshaft pulleys (a strap wrench helps a great deal here), the rear metal timing belt cover, the CID sensor (good time for a new Wells F134 from AutoZone for $29.99), the CID sensor's mounting ring and the sensor vane screwed to the camshaft's end (remember which way it was installed).
You also have to find some way to remove those seals. I used a Dremel tool and drilled small holes in the seal into which I screwed a sheet metal screw and pulled with pliers. The strut tower makes the rear bank exhaust camshaft a challenge. You can get the three direct OEM replacement seals in the Fel-Pro TCS45870 set from RockAuto.com for $14.34 or local auto parts stores like O'Reilly for about $16.
The front main oil seal is the National 710220 from RockAuto.com for $6.26. You may want to swap the lower radiator hose that is the Motorcraft F5DZ-8286-FA from FordPartsOnline.com for $12.87. The water pump gasket set is the Fel-Pro ES70425 from RockAuto.com for $4.88.
When you do the upper engine service you will likely replace the valve cover and plug well seals (Fel-Pro (for '91 SHO) VS50378R, AutoZone.com, $71.99) and the intake to head gaskets (Motorcraft E9DZ-9439-A FordPartsOnline.com, $12.14, 2 required). You should be good about cleaning out the plug wells and the spark plug boots of all that oil.
You didn't mention the oxygen sensors, so unless they have recently been replaced (last 60,000 miles?), you should install two of the Bosch 15716 from AutoZone for $49.00.
That should take care of a lot of present and future maintenance needs.