I have experienced a similar issue with a NS Oscar. The heating element
was coiled and the coils just expanded a tiny bit. One coil was the
primary problem - it was the site of the rupture of the element. The
Oscar has a copper boiler which is pretty thin and bendy, so I pulled
the element out as far as it would go and cut it off, then kind-of
'unwound' the spiral element with two pairs of angled pointy nosed
pliers. The inside of the element had a softish ceramic material that
made a mess but yielded to the bending. After a bit of wrangling, the
remaining coils kind of 'unscrewed out' the hole... I have to admit I
did look up the price and availability of a replacement boiler during
the exercise.....
If the fit is just a tiny bit off, it is probably just scale and oxide
build up. So as suggested: acid. I'd use citric rather than vinegar,
but that's just me :)
Cheers
/Kevin