Yep foil tape works but id say mastic is the right way. A tub will be more than you need, they also sell it in caulk tubes which should be cheaper. Just use any extra on your other junctions too. Hit the ones nearest to your unit which is where your static pressure will be freatest.

Clean energy credit union does modest rate loans. That allows you to get the panels, they foot the up front cost, you get the fed/state/utility incentives and put those towards the loan. That's pretty much your only option other than footing with cash.

I'm surprised no one mentioned this so far: check to make sure the fins on your outside unit are clean.

My parents had this issue when I was visiting. I went outside and looked at their unit and it looked like it was covered in carpet. I took a hose and gently rinsed off all of the dirt and pollen and they were back in action.

Others already covered a lot of good points: make sure it's not froze (it likely is if you've been running for a while and it's not keeping up) and change the filter.

If that doesn't work you likely need refrigerant.