(I followed the instructions of my PEI textured sheet that said "DO NOT WASH" in big red letters. )

All I can end with is your PEI sheet looks dirty and oxidized.  I am not surprised PLA is not sticking to it.

My nearly two year old PEI sheet looks like this - and it's the only side I use... I used a brim on that part because I had modified the model to have a hollow under the base for adding weights - the base only had a 2 mm rim.  

Then, unscrew the nozzle a full turn. This will leave a little space to tighten after screwing in the heat break.

As I mentioned, I did have a new textured PEI sheet that I tried ... and that also failed in nearly an identical way. 

Since adjusting the nozzle didn't change the outcome, it does seem like there's some other problem unfortunately. :(

Unfortunately, it seems like this is a giant waste of time and useless printer at this point. It's too bad that these things can be so difficult to troubleshoot and fix consistently.  I've spent a phenomenal amount of time with it. 😖 I wish Prusa could help more. I'm glad I got quite a few good prints out of it over the last year. 

Thanks for trying.

PLA sticks to a clean PEI sheet very well.  Perhaps it is time to buy a new sheet, do the initial cleaning and see how it goes.  

Some report that a light sanding of the sheet with 1000 grit sand paper works for those who can't get the sheet clean.  I don't recommend it because I've always been able to get the sheet sticky again with soap and water and once in a while resort to acetone to remove the white oxide residue that happens with time.  

At this point I don't believe I am helping.  Maybe someone else has suggestions.

I adjusted the nozzle. 

I ran the PID calibration and tweaked the Live-Z.

I cleaned and cleaned the Prusa printing surface and did a print ... it failed and became unstuck eventually. 

I also tried a textured 3rd party printing surface I'd bought a few months ago when the printer was still chugging away -- I'd never used it though (and adjusted the live-z for that surface). I followed the directions for it exactly. The print failed and became unstuck. 

I was trying a retraction test print this morning and noticed that the surface of the print on layer 3 or 4 was looking rough and fuzzy... I'm not sure if that's indicative of anything. I've got the extrusion modifier still set to 1.025 for the filament I'm using. The part was starting to unstick as it printed. It prints so fast it's hard to tell, but it's almost like it was pushing into the existing filament rather than just putting a layer of filament down. 

The only thing that looks odd about your hot end is the HEX on the nozzle seems embedded to far into the heater block. You might check to make sure the HEX portion does not touch the block. It should stand off a 1/4 turn minimum.  If it is too high, too tight to the block, the heat break is too high and might cause problems by not seating fully against the nozzle. 

This is the gap that should be there.

I don't know why there are loose strands unfortunately. The strands aren't always adhering to the previous layer. I only made the one change between the two prints, the extrusion multiplier. 

I think these issues were starting to happen before disaster struck and caused the damage that resulted in me rebuilding parts of the extruder assembly. I did follow the guide for the E3d-v6 that was provided by Prusa to me. 

What visual signs should I be looking for to determine I'd need to do the acetone scrub? I need to wait on buying more parts but could try the scrub.

There's no audible clicking during extrusion that I've heard in some YouTube videos.

Here's what I bought to replace:

 When trying to disassemble it, the heatbreak snapped in two pieces (there was a giant mass of hardened PLA filament). So, I also bought a 

Prusa MK3 Heatbreak

Prusa, via chat, provided me with the links and clarification I needed to reassemble the parts. 

I took this photo last week when trying to troubleshoot the issue with Prusa chat. I don't have one right now without the silicone sock. (I've not used the sock during these recent tests).

FYI - There's some filament "residue" baked in at the back -- it's not leaking, it's from the giant filament ball that destroyed the printer. It's cosmetic -- I scraped away what I could safely.