We had our home inspector and also had our U&O Inspection’s (heat, chimney and electric).

I suspect your condensation problem relates to heat escaping through the old roof and meeting the cold air. 

In winters I am positive that the heat cranked up higher than normal.

I have been living in one of the unit and renting out other 2 units which covers the mortgage and I’m just paying utilities, heat and water bill out of pocket.

For example, if it is a couple middle aged guys then you could let them sweat a bit, but if it is a little old lady that is sensitive to heat exhaustion, I might replace it sooner than later. 

We hardly ever open windows down here in the deep South because of the heat, but if you have a ripped window screen, you will fail the inspection and the property will be disqualified i.e. you don't get paid anymore from Section 8 if you don't fix before the re-inspection.

Would you rather get infront of it, or would it be better to wait and hope it lasts until its warmer to not shut off heat for a day?

@Pierce Conway I just converted a 3 unit building from a single gas boiler (with cast iron radiators) to 3 separate mini-split AC/Heat systems.

Literally two weeks ago, one of my best friend's wife goes to a property that I told him not to buy, 5 squatters were partying in it, heat was up high to 90, and he ended up fixing what they broke and spent 10K. 

If it's electric then they should not be taking the covers off the heating elements and messing with it.