Must bibliography entries match the original title's German orthography?
I would always prefer the original title of the paper (only ignoring all-caps or similar), even if it contains spelling mistakes, as this is the most likely search term, somebody is going to use (and not all search tools do autocorrections). This in particular applies to titles in spelling conventions that readers might not be familiar with. A German paper from that time might use the spelling Oscillator instead of the modern Oszillator or Maasssystem instead of Maßsystem¹ – would you also change these?

As a sidenote:
Uppercase umlauts (such as Ü) only came up in German in the nineteenth century and were only fully established as a consequence of the spelling reform/establishment of 1901. Thus, it’s very unlikely that Ueber was used due to typographical restrictions and one could argue that it is the more correct spelling here. Also note that nowadays, substituting Ü with Ue is only allowed as a makeshift solution and the two are not regarded as equivalent.



¹ Taken straight from Max Planck – Ueber irreversible Strahlungsvorgänge.