Mathmos formula changes during the years.
Did you mixed old wax and recent liquid?
Try to remove a 1/4 or a 1/3 of the liquid, and replace with water (distiled if possible).
Keep the liquid, in case you remove too much of it, you'll have to put some of it back.
Yes it should.
You just have to find the right amount to replace.
Start by removing a 1/4 of the liquid, it should be OK.
(and keep it safe until the lamp is repared).
Have fun ;-)
I hope so!