1988 Ford E-Series Van I posted query and paid for answer b

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Problem: E-250 Van Auto, A/C, fully serviced, recent complete tuneup, new plugs and wires, oil change, all fluids checked. Now is emitting odor thru front grill at left side as you are standing outside, facing van. Heat gauge not above normal.

Radiator full and fluid clean. Oil a bit dirty altho changed 500 mi ago. No oil or other fluid shows on paper towels we wiped under van. Serpentine belt seems taut. No unusual noises.
New calipers; brakes flushed. Differential checked.
Rear end fluid checked. Bearings packed. Wheel hubs do not feel abnormally hot, besides, smell is much higher up.

Smell is not exactly like oil or rubber. But heat and odor means either something flammable is in contact with heat, or that there is friction, Right?

What possible causes do you suggest checking?
Could an engine gasket be failing?