I often wonder how much extra it would cost to fit metal gears instead of the splitting prone plastic ones; I suppose they hope to make more money on spares and/or repairs.
I think that's rather cynical to presume they use poor gears just to encourage the need to buy spares.
Brass gears probably cost a bit more as I guess they have to be machined not simply moulded, but there is also the argument that plastic/acetal gears run quieter and don't wear like un-maintained brass gears may do (I've come across a few worn out brass geared locos, totally lacking in lube and with brass particles thrown around the inside of the chassis block :( ) With the plastic gears they just need to get the interference fit correct, make them thick enough, and use good quality material so they're not under too much pressure and split.
I still prefer brass gears though. In the Continental sub-forums I've documented replacing 12 plastic gears with brass on two locos over the past 2-3 weeks :D Particular models are known for problems with splits (it's not just Farish) hence 3rd parties such as KH Modellbahnbau have developed kits with compatible replacements.
If the market were there, perhaps an enterprising small firm could create upgrade kits like the KHM ones but for Farish locos? It's just a case of knowing the relevant measurements. I think I read somewhere that KHM themselves had to place a minimum order of 500 gears of each size needed. I found old posts on German forums where the late proprietor of KHM used to discuss gear problems people were having and if identified as a persistent failure he'd look into sourcing brass upgrades.
Actually, I think the Polish firm KKPMo I've used in the past for custom acetal gears can also produce them in brass, but they'll definitely be expensive. I only used them as a source when I couldn't find any replacements at all.
I still have some early Farish diesels with brass gears and they are still running without problems. I fitted 5 pole motors in them over 10 years ago and I oil them regulary, depending on use.
@Bobro (https://www.ngaugeforum.co.uk/SMFN/index.php?action=profile;u=818) Yep I loved my original brass geared Farish class 47 (with lights too :) bought brand new when they first came out. I did actually sell it on to a friend when I changed to Continental N in the 80s (he's still got it AFAIK), but have since bought a mint replacement :D
Proper gears....
(https://www.ngaugeforum.co.uk/SMFN/gallery/113/5885-310821144556.jpeg) (https://www.ngaugeforum.co.uk/SMFN/index.php?action=gallery;sa=view&id=113294)
(https://www.ngaugeforum.co.uk/SMFN/gallery/113/5885-310821144625.jpeg) (https://www.ngaugeforum.co.uk/SMFN/index.php?action=gallery;sa=view&id=113295)
@Dorsetmike (https://www.ngaugeforum.co.uk/SMFN/index.php?action=profile;u=2855)
Assuming you are referring to Farish then take a look at this and the following posts........
https://www.ngaugeforum.co.uk/SMFN/index.php?topic=6331.msg725596#msg725596 (https://www.ngaugeforum.co.uk/SMFN/index.php?topic=6331.msg725596#msg725596)
It might, just might be the case they've changed to the white gears for the future but as Dr Al says there's loads of stock still out there.