I had one seller inject a seller side broker and pay them 35k commission for doing nothing except holding deposits. 

Shots (injections, pills, compounds) have terrible unintended consequences.

I did get a licensed engineer's evaluation, he suggested that polyurethane foam injections would be a great solution and that failed miserably.  

I think @Brian G. and @Jaycee Greene hit it on the head: an event occurring/debt resetting.When the debt forcefully resets on some of these assets, valuations drop if the submarket cap rate has expanded and/or if the operator can not show a good t-3, t-6 etc due to economic vacancy and rising opex (insurance, r&m etc).If the operator can't inject equity to cover the difference, then trouble arises.

What if you need to inject more money? 

Inject energy into your calls and appointments.6️⃣ YOU’RE AFRAID TO FAILThe truth?

Based on the above assumptions, this will give us a negative cash flow for most years, but because of our cash injections we'll be able to purchase another property by Year 6. 

“Was it really necessary to inject politics into the conversation”I guess the answer for you is yes  

Overall, the conservator has ultimate authority over all operations of the Enterprises.”In exchange, the US Treasury injected up to $200 billion each in capital and owns stock (technically warrants and senior preferred) in FHFA, upwards of 80% of it.

Quote from @Vince Scipione: Yes, they are a popular choice where I live and work, however with the ever fluctuating cost of oil heat, many people have swapped over their boilers/furnaces to what is called a "Propane Gun" essentially it is a device that is affixed to the front of the furnace/boiler that injects the propane and ignites it.