Yeah, but Caltrain isn't a subway, it's regularly old heavy rail. Which, like I said, is not generally deployed in subway systems due to size and comfort issues.
As far as the spares are concerned... Yeah, I'm not really sure what to tell you. It's not a problem limited to BART. Most subway cars in the world are produced by Kawasaki, Bombardier, etc. Even still, I wonder how much other cities with standard rolling stock get to reuse parts in maintaining subways? Perhaps you know.
I don't doubt there are other random parts difficult to find or source. Especially from a system that was originally built before electric train standards fully formed. The cost of innovation is maintenance.
Well, no. Maintenance is the cost of stagnation. Look at New York, Chicago, or Berlin to see how electric rail has evolved over the years. BART is still the only system in the world running 1 kVDC. That means no matter who they buy from there's no commonality. For the most part it doesn't matter that Rohr went under. Although per the article current manufacturers are having trouble recreating the cab windows from the original BART cars - something that didn't need to be innovated on in the first place.
Muni (with a lot of effort) can run a fleet of trams that are 70–100 years old. They've modernized the propulsion where necessary and made whatever other changes were needed for compatibility. Part of the reason that's possible is that Muni runs a 600 volt system which is common worldwide (although largely supplanted by 750 volt setups). These antiques run in revenue and charter service all over the city and yet BART can't find windows for its cars that were built to its specifications.
BART ordered brand new bespoke trains from Bombardier and still uses a bespoke traction system (1000 V DC). Factor in BART's one-off driverless cable car and their standard gauge diesel line. In 15 years when stuff starts wearing out, which agency do you think is going to have a more difficult time with procurement and maintenance?
Caltrain is "heavy" rail, sure. Muni isn't. When they were new the PCCs were used globally (including in San Francisco) and serve as the basis for a number of modern designs. BART set out to be the sexy anti-rail and that's the problem. Fifty years on and they've doubled down on bespoke gadgetry.
As far as the spares are concerned... Yeah, I'm not really sure what to tell you. It's not a problem limited to BART. Most subway cars in the world are produced by Kawasaki, Bombardier, etc. Even still, I wonder how much other cities with standard rolling stock get to reuse parts in maintaining subways? Perhaps you know.
I don't doubt there are other random parts difficult to find or source. Especially from a system that was originally built before electric train standards fully formed. The cost of innovation is maintenance.