I wanted to follow up on this thread.

Has anyone else successfully replaced the o-ring on the lower side wall of the steam boiler? It almost seems impossible. I guess I try using the silicone grease that the OP suggests before totally giving up on this machine.

Ok, I spoke too soon. I was able to fix it with the silicone lubricant. The OP in the thread linked above mentions he had the same problem trying to seat the new o-ring. I guess unless anyone else has had luck without it, this really is a necessary step. This was a really annoying one to fix, but hey, I now know it's doable!

I just completed this repair as well and I'll share a few bits of my experience. I 100% agree with @gchapman on how this could be the end of the road for some people's fix-it-yourself journey with this machine. I've been doing minor repairs (o-ring replacements, solenoid, new steam probes, etc) on my BDB for seven years and with this one even I was looking at whether there were any Rancilio Silvia Pros in stock in the US.

Some things I observed / did to augment what others have already said.
* I'd been hearing the sound of a little bit of steam escaping for a couple of days, and then one day there was a lot of leaking. It took a bit of spelunking to figure out what was going on.
* I originally started using one of the AFLAS o-rings, since they are indeed more durable. But they are also not at all compressible, so i couldn't get the hose back into the port enough to reinstall the pin, and when I was removing it, the o-ring came off. I tried to see if i could fish it out, but after i couldn't find it (since it's black and the hole in the boiler is also ... black) I had assumed that it fell into the Void. wrong. Eventually I figured out that it must be in there somewhere, so i made a kind of hook out of a small paperclip and was luckily able to get it out eventually.
* I switched over to a silicone o-ring and tried to get the hose back in, but the angle of insertion actually kept causing the o-ring to get caught in the gap for the hitch pin, which shredded the outer rim of the o-ring. I tore up a few rings doing this. To remedy this, I removed the other end of the hose from where it attached, which allowed much better maneuverability. Re-installing the other end of the hose at the end was the only non-annoying part of this job.
* I dropped the original pin down into the Void. No amount of upside-down shaking could persuade it to come back to me. Luckily the 7/32" external hitch pins sold at Home Depot in the US do actually work quite well. I bought six of them, and dropped four more into the Void. I might have been more careful if I had fewer
* Taking off the solenoid did help quite a bit.
* +1 on the silicone lubricant
* Proper lighting is key
* This was just really annoying. The position, the lack of visibility, the various things getting in the way. It reminded me of changing the driver's side spark plugs on my Jeep, which basically require removing the engine (okay, i'm being dramatic, just the intake manifold). It just feels like it was not thought out how someone would repair this easily.

Did anyone have trouble pulling out the tube from the side wall? I easily pulled out the other end of the tube, then threaded it through the maze of other tubes/wires until it was almost straight horizontally (for max pulling efficiency), but can't get the other end to come out. There looks to be some mineral deposits/calcification around the port. Can I put some type of liquid drops on the port to loosen up the connection point? I'm almost about to give up lol

I had the same problem of the tube not coming out because of the calcification/deposit issue. I used a drop or two of vinegar to help dissolve the deposit plus used a wet tissue over it for about 15 minutes. That worked.
Yes this particular O-ring replacement was a royal pain. Felt fortunate in the end that everything came back together without leaking.
BTW: I didn't need to perform this repair until the 5 year point of ownership. Machine has always been heavily used but with low hardness water.

Thanks for the tip but unfortunately it didn't work for me. Was your tissue wet with water or vinegar?
I was literally pulling the entire machine sideways, that's how stuck the tube is.

The tissue was wet with just water after using a couple of drops of vinegar on the "crust". I was actually amazed that the crusty deposit was there since my water source has a hardness of 1, but I figured that after 5 years anything could happen.

Hi All found you after trying this repair on my oracle. I had almost the exact same issue, the machine was tripping my electrics and I found the Teflon hose half way down the boiler with mineral deposits so bad I couldn't remove the hose, I ended up snapping the Teflon hose and had to end up tearing into the machine to free up the boiler to get access, its currently in about 200 bits and I can't find a replacement hose for love nor money, I believe the part number is: SP0001651. Sage UK have said its out of stock and no idea when it will be back for sale. Do you happen to have a source for parts or have an idea where is could get the pipe and brass fittings to possibly make my own please?

One thing you could do is order any tube assy available from Sage/Breville with the correct diameter and fittings and a push lock coupler. Cut one of the ends off the new tubing with enough lead to couple to the existing tubing. Not optimal, but serviceable.

this is a good idea thanks