Flipper had work done on it in March '21 but in the last couple of months a few external cracks have grown and internal cracks have appeared.

the last part of that sentence is where the issue lies. you have to get into a habit and routine of putting in the hours for yourself. you have to find the motivation either internally or externally via somebody else keeping you accountable at the end of the day the question you have to ask is "How bad do you want it"? 

@Genny Li has the best idea, albeit the most expensive :-)If you choose to go with adding an external condenser to your current FAU system, you will probably have a problem with the duct size.

So far this year, it's covered:Porter services for bulky trash removal for the 108 units.Paying off the loan that was used to replace all the vinyl siding with LP Smartside on all the units and paint them.Maintenance and repairs on all the external fire alarm system stuff.Regular landscaping.Tree removal after the big freeze.Regular powerwashing.Weekly litter pick up services.Pool services.And that's what I can think of off the top of my head. 

That puts you in the low end of that 3-5% range to essentially just break even from any external economical factors increasing your expenses.

I hand picked him years ago for the ADU at the B&B and he moved to the duplex with me.

Then we hand pick a few people to send mailers to.Door knocking can be effective especially if you have something of value to discuss i.e. a recently sold, Under Contract or recently listed property nearby. 

Are these dampers accessible externally to adjust or it requires opening up the ceiling?

We as Americans just can't seem to keep external things like depressions, wars, credit crises, elections, stock fraud, pandemics and all the stuff of life from interfering with a good real estate market. 

We bought it because it also has a 1000 sq. ft external garage that has a split HVAC unit in it and used to have plumbing maintained in it.