Nice truck! My '91 FJ80 was one of my favorite trucks ever.
The engine side (pushrod gallery) cover gasket and the oil pan gasket are two very common leak points on the 3FE. Replace them only with OEM Toyota one-piece cork gaskets, and do not over-tighten them (FSM spec is only 83 inch-pounds IIRC).
That's funny! I had my mechanic replace the gasket in the oil pan b/c of a leak and he didn't use the Toyota one-piece the 1st two times. He had to re-do it 3 times, but now it's stopped leaking, finally!