No stupid questions around here....
The HP resevour is the silver thing on the very top, front of the motor, dead center. It is just in front of the fuel filter housing and just above the water pump. On the drivers side of it there will be an allen plug that you will remove. Be carefull to use the right size allen wrench as the metal is very soft and will strip. Once the plug is out, check the level with a screwdriver. There should be oil within an inch or less of the top of the resevour.
Another possiblility here is you may have injector o rings going bad. It is a relatively common problem on the earlier 7.3's through 1999 or so. There has been an updated o ring kit to prevent this put out since your truck was built....
We will get it all figured out though....just out of curiosity, do you have a block heater and have you tried seeing if even during warm temps if plugging the truck in makes it start better??