only a light closing pressure is needed to achieve perfect seal.
never close the cap tightly
if you close the cap tightly, more damage can occur when the pen is dropped.
tight closing of the cap will put excessive outward pressure around the thread area.
drop shock + tight cap pressure will increase the chance of cracking.
even if the eureka cap thickness (thread area) is quite thick,
excessive cap tightness + forceful drop can cause damage.
this is same for all the pens out there with thread closing cap.