Got a cheap 2nd hand NS Oscar, which I descaled (perhaps too aggressively), after which a small leak near a fitting in the boiler appeared (or maybe it was already there before descaling). You can see the problem here:

https://photos.app.goo.gl/BT2frKc1kp48hN4u8 (video)


Two questions:

1) Can this realistically be fixed by a sealant, e.g. Loctite 290?

2) What are the potential dangers of a leak like this? Will it simply impact the boiler pressure if it gets worse, or is there risk of explosive boiler failure?

Thanks

Seriously doubt any type of sealant can safely/effectively fix that. I would look into some type of mechanical fix as in welding/brazing if the material in that area is strong enough to support that. Don't blame yourself in the descaling aspect as the boiler looks to have been subjected to far worse treatment leading up to this issue.

The quick answer is you can fix it if you have the equipment and skills needed. You need to remove the boiler and vigorously brush away all the corrosion and then braze a new bead around the base of the fitting where it attached to the boiler (or if the fitting is shot, replace it with a new one).
15% silver brazing rod ought to do the trick. Or just replace the whole boiler.

Matt-
Looks fixable assuming that is the only leak you've got. Member "pressino" provided you the means/method to fix but based on the condition you've shown I suspect there are plenty of other pinhole leaks present. If you do go through the time and trouble of removing the boiler and doing additional leak checking it might be better to just go ahead and replace the boiler with a new one - it's probably the most conservative and safest way.

As you are in Europe, elektros.it should be a good source for the boiler although at the moment they seem to be out of stock of the Oscar/Musica boiler (they're the same p/n).