85' W350
 

360 w manual, need info; how to replace oilpan gasket and main seals...is it necessary to remove exhaust or cross members???

most of the time you can drop the pan and remove it by spinning the crank so the counterbalance weights are clear of the pan too remove it.
then you can replace your pan and main seals.
but while you are in there you may as well plastigauge the bearings and replace them along with the oil pump.
then i use a longer set of bolts with nuts threaded on them to set the ends of the oil pan it takes a bit of pressure to push the pan on and this has helped me in the past.
post pics and keep us posted

W350 is a 4x4 3/4 or 1 ton. There is no room underneath to properly remove the oil pan. It's easier to unbolt the engine from transmission and pull the engine.

Before you get into that though the rear and front main seals along with oil pan hardly ever go. At best they seep. If you have oil in those spots chances are it is valve cover gaskets or the oil sending unit leaking instead. The front alone would be the fuel pump leaking oil. Best to check these both BEFORE you go to all that work.

I would remove the engine too... Go through it Replace every gasket !!! and the timing chain..
A lot of time the intake end seals leak, or dist O ring Drips down off the oil pan

X3 with removing the motor. The W350 is a 1 ton but all the trucks have a cross member that run under the oil pans. Clean the motor and verify that the oil pan gasket is what is actually leaking and not something from above it.

If you do have to pull the motor, I'm with TV on going through and replacing a lot of the gaskets and timing chain while it's out. It's much easier than when it's sitting in the vehicle. Also, take a look at your clutch, flywheel and pilot bearing and address those too if needed.

Addition since it is a stick, I would check the center main bearing thrust surface while the pan is off..

I should have said rear main seals:)