But you achieved higher status in the home espresso world than your friends who cheaped-out with their mere Rocket machines, so it's worth the aggravation.

There's some truth in the cynicism of that observation, but let's be honest: Unlike some home appliances, many high(er) end espresso machines are easy to maintain and repair; E61-based espresso machines like Rocket are among the easiest. Thanks to online forums like this one, Reddit, Facebook, etc., owners who want to do their own work can ask for help and get detailed instructions.

Back to the OP: Two years is enough time for untreated hard water to cause the reported problems. If scale buildup is indeed the cause, it may be significant enough that a teardown is required. For most owners, that's beyond the DIYer's abilities and is best left to a qualified professional.

We don't descale in Seattle. Total Dissolved Solids out of the tap is about 45ppm.

This is not about La Marzocco Línea Mini. My less than 2 years experience was with a prosumer the M&V Vesuvius. Purchase this machine with a price tag of $4500 (not the 7000 of linea mini but certainly above the lower price of ECM Synchronika or Profitec with pressure profiling). Less than a year of home use the heat element of the service boiler had to be replaced, it failed just like that. About 4 months later the temp sensor had to be replaced, the sensor is made of some form of copper like metal that is prone to chemical reactions at low ph I was explained by the service technician. I use reverse osmosis water with quite low PPM. I was surprised as I used a Breville machine with the same reverse osmosis water for more than 10 years without any issues.
Just 1 month before the machine being out of the 2 year warranty it started displaying a service message. It lasted about a month then there was no water flow through the group head. Pressures were there indicating the water reached the boilers. There was obstruction to the water flow somewhere in between. I did maintenance to the head group expecting to release the obstruction at the mushroom pin hole.
No resolution, I found green degradation of the chrome metal inside the mushroom of the group head, and I found metal scraps lodged in the terminal strainer from the hot water wand, the one that comes from the service boiler that works correctly.
Now my machine is waiting for a trip to Austin TX to receive professional paid for service. I would have ship it for the job to be done under warranty in New York if not for the $600 price tag each way for shipping it.

What TS wrote sounds just normal maintenance. Not sure how water quality is but it could be you are the cause of these "problems". Having a bit of scale if inavoidable but if you treat your machine well and do the monthly maintenance you should be good. Espresso machines require maintenance and those higher end machines require a bit more maintenance then an E61 but they also deliver much more. If this is all you had in nearly two years then it's very minor and surely nothing to complain about.

What I read is an owner with unrealistic expectations and not a problem with a particular espresso machine. People just buy expernsive stuff without doing the homework and having realistic expectations of what you could expect in terms of maintenance and use. LM advices for maintenance every year but a certified technician so have you done this? If you're not comfortable doing small repairs then you should hire a professonial every year to do the maintenance.

This is like buying a Ferrari or Lamborghini and complaining about it needing more maintenance then your friends Lada .