Great tip there Graham, but what this also likely suggests, is that the lampholder itself is probably overheating from insuffient cooling air if the fan on these machines is somewhat weaker than it's rivals.
Once this happens, the inevitable is that the brass ferrule inserts inside the lamp holder become "baggy" from too much expansion and contraction.
This, in turn, leads to poor contact to the lamp pins and then arcing, thus vastly shortening the lamp life.
Typically the lamp pins on replacement will appear blue in colour along some of their length or even pitted or eroded altogether!
I wouldn't mind betting that if the lampholder was replaced with a brand new Bender & Wirth type, you would experience something like the same 50hr lamp life that you get from these very same lamps with all other models in good health, set at the correct voltage. (might be slightly less if the lamp is constantly running extremely hot, but not too much I'd say).
Good conductor contact is imperative on a 10 amp circuit, throughout the circuit!
A poor fitting lamp holder is effectively a miniature and primitive arc welder, and that's not what's wanted here at all!