FWIW: (Warning, unsolicited advice ahead...
) That 52 year old beastie-boiler probably had a steady-state combustion efficiency of no better than 80% on day-1, and that was BEFORE all of the rust, scale and corrosion on the heat exchanger plates of a half-century of use. If experience in my neighborhood means anything, odds are pretty good that it's 3-4x oversized for the actual loads, which means that even on day-1 it's as-used AFUE was probably something around 70%. Today it's steady-state efficiency might be as high as 75%, but it's probably lower, and with cycling & standby losses you're probably only getting 60% out of it.
Even though the price of natural gas is currently near record lows, at any fuel price it's probably time to retire the thing and put in something that is
A: Sized for the actual heat load at the 99% outside design temp. This maxes out both efficiency AND comfort.
B: Higher efficiency (even if it's an 85% cast-iron thing, rather than a modulating condensing boiler.)
Even newer-better cast iron boilers sized to your load would cut your fuel use by about 30%. Depending on how much radiation you have relative to your peak load, a mod-con boiler would probably cut it by about 40%, maybe more.
Since the thing is still able to heat the house you have time to carefully consider your options and save up for it, make a plan, maybe even dig up subsidy money for it, if there is any available from the utilty or state. (It's a moving target, I don't keep track.) With a couple of heating season's fuel use behind you, it's possible to put an upper bound on the size requirements of any new boiler by the ratio of fuel use per heating degree-day, using boiler as a measuring instrument. It's most-accurate if you have gas bills from mid or late winter, on periods where the house was occupied the entire period between meter-reading dates (not the month you spent 2 weeks surfing in Belize with the thermostat set to 50F.)
It's much better to have a pretty good idea of what you need BEFORE the thing bangs & clangs for the last time, cracking a heat exchanger plate and dribbling a steaming load onto the basement floor. That way you won't have to make hasty decisions under pressure and end up installing another wrong-sized boiler that'll be there for the next 20-50 years. The typical boiler installer in an emergency-hurry situation would come in and just replace it with something of equal (sometimes slightly greater) output and call it a day. While that method of boiler sizing would still keep you warm, it would be a mistake on both efficiency & comfort grounds, and would cost a bit more up front to boot.
As long as the existing boiler keeps chugging away there is little immediate incentive to change it out unless the price of gas skyrockets. But I've retired functional boilers less than 1/3 it's age when 4x oversized (and I'm not in the biz), without regrets. The cash to do these things may not always be readily available, and you may have to prioritize differently, but a boiler that old isn't worth fixing once it starts to go- it's realistic service life was already up by the end of the Reagan administration, but since it hasn't failed catastrophically, it has been left to the "next owner" of the house to deal with. There are much older and even more decrepit boilers than yours still in service, I'm sure. But if you intend to live there for awhile, it's worth having systems that you're not always picking away at and worrying about.