Ball oilers are interference fit in a plain bore, Drip feed or cup oilers are likely to need a threaded hole, so you will need to make adaptors.. And will stand proud of the surface.
Will this mean that they get sheared off at extremes of travel?
I have had ball oilers on my Warco Mill/Drill for nearly 30 years, anon my Engineers ToolRoom lathe for almost 20 without problems.
And I tend to be fairly heavy handed.
Maybe the OEM fittings were built down to a price, rather than to a quality?
FWIW, my advice would be replace with ones bought from Arc Euro, or Warco. They might be more durable.
If you break those, it might be the treatment that they get.
What sort of oil gun are you using? and how vigorously?.
Howard