Someone who has done maintenance on a Duetto II:

What size wrenches do I need to open the top of the group to check for scale? I measured 35mm and 22mm, but want to be sure before I buy anything.

While we're at it, what size wrenches are need to pull the lever out?

Go any buy yourself something like these:
These will do most of the small nuts
https://www.amazon.co.uk/Hilka-16600802 ... nd+spanner

This is for all the nuts on the group and steam wands, because they have the plastic jaw protectors
https://www.amazon.co.uk/Amtech-Adjusta ... protectors

1 large Box spanner for the heating element I think it's 38mm, but you need to check. It's tempting to use a crowfoot, but a box spanner is better as you get a more even force on it. I actually use a large 38mm socket (with my impact gun) but they can be quite expensive and you have to be careful.

The above tools (I assume you already have a cross head screwdriver or two, will allow you to do any and all jobs on the Duetto MKII. I assume you can find all these things on the US site and probably cheaper. A kit like this will set you back around $35

The machine should be serviced once per year, open the top plate (4 screws), look and see if it all looks good...if it does, close it up and don't interfere. If it's leaking or any burnt connections deal with them. The E61 group should be lubricated every 3 months, or after any cleaning backflush. Apart from that the group only really needs maintenance when the lever spindle leaks (2 small round washers), group gasket leaks (you should have some spares change every 9 to 14 months) or one of the 3 group valves is leaking (you can replace the rubbers sometimes, but usually whole valve needs replacement.).

On a MKII one very important check is that the pump is not leaking into the motor. Undo the clamp open it very slightly, just enough to shine a torch in and look for leaks, if not push together again and "nip up" clamp. When I did the top level design for the machine I wanted the pump the other way up in a cage (I even did the drawings for it), but they wouldn't do it. The latest model Duetto (MK4) finally has this revision. If the pump is leaking, simply replace it. You should get 7+ years out of a pump, but some can leak much earlier.

I built a leak detection system for my MKI, this is effectively a small wick with a soluble blue line on it, put through the weep hole of the pump. I placed dow corning 111 (fair bit) around the motor spindle at the base, then stuck the wick in this. If water comes in any quantity the wick will soak it up and blur the blue line (this I can see from outside the pump). I also wanted electronic low water detection, this is also achieved quite easily and I got rid of the stupid sprung platform on my MKI.

Here ya go:

Thanks Dave and Eric, this is very helpful! I may have some work to do.

I've owned my Duetto II for six years, and I've done very little preventive/routine maintenance on it. I've lubricated the lever and cam once when it got a bit stiff, replaced the grouphead gasket when needed, dropped the shower screen a few times (but seen no residue build up), water backflush after each session, and a detergent backflush once in a while. I do not have hard water, and have perhaps been willfully/blissfully ignoring the possibility of scale, so have never opened the group to inspect the mushroom. I did recently notice some spots of scale in the end of the hot water wand, which got me thinking about all this.

I do open the case at least once or twice a year, usually to adjust the pump (and have replaced the PID twice). I haven't looked as closely at the pump as you recommend. I've never seen anything that looked like a leak or burned connection anywhere else.