I have gas furnace so heating runs on gas. Is hiring a hvac contractor to do maintenance tune up to prepare for the coming winter recommended? I understand that experience and opinions can vary, but I'm thinking the older your heating system the more it would be recommended, but I don't want to pay anywhere from $50 to $150 for it to be a mere sales opportunity for the hvac contractor.

Furnace runs fine than there's a little oil smell I cleaned it and watched it run burner runs good blower comes on no issue burner shuts down blower running smoke comes from around combustion intakes by oil pump burner comes on smoke stops when I lift transformer sticky oil residue is covering it and seems oil is possibly blowing back from nozzle checked chimney it's clear also pulled chimney off furnace clear so I lift transformer put grill lighter in there by nozzle draft pulls flame slightly into chamber turn blower on it pushes back towards me flickers and goes out I'm thinking bad heat exchanger am I correct on this?