I believe Gerstlauer make replacement Schwartzkopf parts. Can't remember where I heard that though. A lot of engineers moved between manufacturers (e.g. arrow and RMC) and I believe originally some went to Gerstlauer, not 100% sure though but defo heard somewhere that they supply parts for them.I think my thought process was that maybe some of the larger metal parts of the trains and wheel assemblies were difficult, or maybe even impossible, to source replacements for. All metal mechanical parts have a finite life, even with proper maintenance. My thoughts were based on an assumption though, and so probably not correct at all. But I never meant to imply that Schwarzkopf's were dodgy.
Would be interesting to know how readily available all of the parts are, given the lack of an OEM manufacturer and the ever reducing customer base for any aftermarket manufacturer of such parts.
EDIT from Wikipedia: "In 1981 Hubert Gerstlauer, a former employee of the Schwarzkopf GmbH, founded "Gerstlauer Elektro GmbH". With this company he delivered electric and pneumatic equipment for Schwarzkopf's facilities. After final bankruptcy of Schwarzkopf in 1992, Gerstlauer acquired part of their production halls and continued the manufacture of amusement rides and roller coasters. The company was renamed "Gerstlauer Amusement Rides GmbH" in March 2007."
Also found a quote from a post on TPR claiming that Maurer-Söhne and SAT-Rides also make their parts.