Super glue and heat or steam are IMO no good mix...

Cyanoacrylate does not do well at elevated temperatures.

What's the harm in trying? If it doesn't work and the cap once again continues to spin, then go to a more radical solution. If it does work, then you've got a easy fix.

So unless the threads don't hold for some reason--a separate issue from the wooden cover--I fail to see any danger to man or beast.

The "harm" is it will fail and cyanoacrylate is not the best gap filler either.

Well then let's put your prophetic powers to the test and see what happens. Better living thru science!

That is not science, it is a one-off uncontrolled anecdotal test.

Yep. Pretty much like your one-off, uncontrolled anecdotal prophesy about failure.

BUT...why quibble? The next time my cap loses its grip, come on over to my place and we'll give it a rigorous, objective, tightly-controlled, double-blind test and see what happens. Could be lots of fun...I'm sure.

Fellas, this is about what glue to use, right? I'm putting this on cooldown for a bit.

First and foremost, I would like to thank every one who responded to this thread. Your taking time to offer solutions deeply appreciated.
Here is a quick update.
I tested that akfix product after my post to this thread and I can easily say to stay away from it. The test was done with a wood piece and plastic piece (not on my boiler cap). Test result was a proof of what OldNuc stated before "Silicone does not bond well and will probably fail soon if not immediately as it is highly elastic". Applied as recommended on product label, let it sit overnight, the next day I was holding 2 separate pieces in my hands Now I have a better understanding of this product, it can be used as gasket but it won't hold up to even the tiniest bit of force applied. So, anyone who gets similar problems in future, simply pass this product or anything similar for that matter.

Next I tried super glue, and no, I had not read your responses yet when I made the decision. So I did the same test and it hold up. Since the main concern was if it would hold up to heat or not, I would not be able to see it without testing on the actual product. Which I did. It works just as RioCruz suggested, but in the long run I am 100% sure OldNuc's prediction will come true and I will be holding 2 separate pieces in my hands again.

You may wonder "Is she crazy? Why she did it? Why not search for a better alternative".
Unfortunately, I can not import any type of chemicals via mail. This may sound strange but in recent years our custom regulations changed a lot and even mailing a small amount of coffee is problematic. This also depends on where you are living and the post office servicing to your area. My luck, mine is extremely nosy. After losing several packages (puff gone, nobody knows when you ask) I am discouraged. Since the other option would be changing nationality, I chose the easy way out, which is asking from friends who live in abroad.

Anyways, thanks to drgary, now I have a source for Pavoni boiler knob with brass thread, so I will be ordering from them and have a friend bring it to me on their next visit (drgary a huge THANK YOU!). Until then I will use this temporary fix, because I have 5lb of delicious coffee which I don't want it to go waste, because I am staying at another place where I do not have access to my Epoca (you have no idea how much I miss you baby..)

All that is said about glues, I would like to take time to comment on the quality of recently manufactured La Pavoni lever machines and the company itself. Experienced first hand, I can easily say every single piece of this brand new machine is failing.

a) Manufacturer did not respond neither mine nor the vendor's emails for a long time. Later on we received a response simply stating "it is what it is, nothing we can do". I disagree with that, you can easily go back to using quality material! Also let them know what I thought.
b) The cover for the sight glass went dull and blurry with heat and regular use (I will post before and after pictures later).
c) Every now and then I have to open & fix the pressure valve so it won't stuck and keep releasing steam non-stop (which prevents the machine from operating).
d) Saved the best for the last. Group head to boiler joint (that rhomboid shaped section) is leaking during pulling shots! How awesome is that?!? (again I will post pictures later)

I am never ever buying another Pavoni product. Never! And I guess I will go ahead and Frankenstein the current one slowly in time.
So, the short version, you guys were not kidding when you said Pavoni went cheap in recent years.

Once again, thanks to everybody, and drgary, I can't thank you enough!

Cyanoacrylate is rated for a max temp of 180F to 225F depending on formula. The top of the boiler is at the highest temperature which is real close to 250F and this is why this bonding agent eventually fails. The Gap filling ability is also quite low as well so if the knob actually makes decent contact with the stem it may hold reasonably well for a time long enough to get a good replacement. If it actually bonded then the gap was small enough and that is probably not going to be the primary cause of failure.

I am aware of all the odd import restrictions that all countries have in place and the problems they cause in trying to import or export something simple.

At least you have a permanent solution on the way.