It's not the boiler that's using the oil- it's the burner, in whatever
state of adjustment (spray-tip-size, etc.) and tune it's in.
The boiler likely would benefit from changes in heat-exchanger design
that have occurred in ~40 years, and cleaning on firesides and
water-sides. Not to mention automatic stack damper, reduced aquastat
setting, and installation of separate domestic water-heater.
You don't mention the burner, and what it's up to. I'd get expert
Yes, yes, yes, seal and insulate everything. Especially at lowest and
highest elevations of house. Chimney effect.
Install programmable t-stat, and go for max setback & lowest settings
Automatic stack damper can yield huge reduction of energy waste,
especially if you're in, say, Minnesota. Or are you in Montgomery?
Existing burner and furnace, if in decent health now, can survive much
longer once you take serious conservation measures, and reduce the
run-time. Then you can plan/budget replacement at a better time-