Loss of braking - replaced lines, booster, and vacuum pump seals.

I have an 02 Golf TDI. I have been having a ton of problems with the brakes over the last year or so.

First I replaced the brake booster vacuum line that had a crack in it. That fixed it for a while.

Then I had another loss of braking and the hissing from the brake pedal. I replaced the brake booster and bled the brakes using the Vagcom including the ABS sequence. That fixed it for a while

Then recently the brake pedal went hard and I had loss of braking again. I replaced most of the vacuum lines and the seals in the vacuum pump. I also sealed the nipple on the vacuum pump with ultra grey and replaced the vacuum line from the brake booster again (because I broke the smaller nipple at some point).

Now I am at a loss to find the issue. The car isn't worth going to a mechanic to if I can't fix it myself.

I am on the verge of getting rid of the car at this point because I am tired of fixing it. It also needs to have the intake cleaned out as the EGR is sticking and is already beaten to **** due to several hit and run accidents that I've fixed with junkyard parts and JBweld. I was hoping to fix the brakes and commute with it another 10,000 miles before the headache of cleaning the intake (if that is even worth it)

Any ideas on how to diagnose where I am losing vacuum? before I give up and get rid of it?

Put a vacuum gauge on the small vacuum line that feeds the rest of the small lines and see if you have 20+ inches of vacuum.
If so do the brakes work now?
If not plug the big vacuum line and see if you have vacuum.
Where are you getting the booster from? New, used?

I agree, you need to see if your vacuum source is good first. The booster is a pretty simple device.

That plastic line probably cracked or leaking again