For Mr. Beardmore:
The type of prints you make have a lot to do with waste build-up in the
LaserJet 4/5 model cartridges. There is no spreader auger in the waste
to distribute waste evenly so if waste is formed unevenly by the
prints, build up can occur towards one end or the other of the waste
bin and eventually cause failure, Additionally the toner is being
constatly heated by the fuser assembly (next which it is located when
the cartridge is installed) and the heat will cause blocking of the
toner (formation of large chunks) molding it into position in the waste
bin.
Your model has a larger waste bin than most cartridges, and of all the
HP models could probably survive the longest in a drill and fill
situation. The 4L, 4P, and 5L on the other hand will fail almost
immediately on the second refill as the first two uses (the original
and first refills) will literally pack the waste hoppers with toner.
Models like the 3si, 4si, 5si, II, IID, IIID have spreader augers which
were powered by the OPC drum rotation so re-using the cartridge without
cleaning the waste bin was known to cause the cartridge to lock-up,
stripping gears in the cartridge and the printer, This was why drill
and fill was frowned upon early on, design changes in newer cartridges
(removing the auger from the waste bin reduced manufacturing costs)
make "drill and fill" less damaging, but does not eliminate all the
draw backs to "drill & fill".
Frankly the 4/5 cartridge is easy to separate into two halves (two
screws removed releases the holding pins) and the bin is easy to open
and clean, I can however understand why you would want to melt a hole
in the toner hopper, since the original fill hole is not accessible
without splitting the toner hopper and the only other way to fill it is
by removing the developer roller and pouring the toner into that
opening.
However, another advantage to disassembling the LaserJet 4/5 cartridge
is that you can clean the doctor blade, removing small paper particles
that collect on the surface (picked up from paper dust in the printer)
and create fine lines where toner is missing on the developer roller.
This is not a large issue with text only printing, but cleaning the
blade prevents early degradation of line art, large fonts, and graphics
which require a higher density of toner for optimum fill, detail and/or
contrast.