The bottom bracket of the bike I'm working on (see my other thread) is toasted, so I've been to a couple of shops asking for parts: it seems hard to find an exact replacements, though. The spindle dimensions are, to the best of my measuring skills, 34/57/40 mm, so 131 mm total length.

One shop offered a 130 mm replacement with a shorter central section (the one called "B" on Sheldon Brown's site), probably a couple millimeters. They said it's not a problem. Also the current cranks (Ofmega) have nuts, while the replacement spindle is hollow. They said this is not a problem too, and that bolts are better.

The replacement has 9-ball bearings (same as the original equipment) which I read are not as good as 11-ball or cartridges. When asked, they replied there are no BBs with 11 balls (Sheldon Brown disagreed) and that cartridges only come with shorter spindles (I've found an online shop carrying a Sunrace BB with a 131 mm spindle).

Did they lie to me about the rest too?

Last but not least, all the specs of the Sunrace seem OK: spindle length, shell width and thread. Is there are any other reason why it wouldn't fit on my bike?

You have an asymetrical BB. Assuming the 40mm is on the drive side, you'll need one that is a 137mm (that is the measurement without the threaded sections). One with crank bolts instead of being nutted is fine (and most likely what you'll be able to find). Number of bearing is important but some of that depends if you have a carrier for the bearings or use loose bearing. You can usually get at least one or two more balls in without the carrier. I doubt the shop lied, more likely they were just ignorant of all that is out there.

Vintage cranks tend to use longer spindles because of the way they were made, but 131 mm is longer than I've ever seen. You should remeasure that spindle before you buy anything. Don't include the threaded portion!

Nutted spindles are usually found on cheaper bikes, with the exception of the Campagnolo titanium spindles that were discontinued because they tended to snap in half. Hollow spindles are lighter and lighter is good.

Your Ofmega crank may require a spindle with an ISO taper. Most of the square taper cartridge bottom brackets available today have JIS tapers. I have a couple of exceptions on my bikes. One is a Swiss EDCO. The other is Miche Primato. Check Sheldon Brown on that subject. It can really complicate things.

Your bottom bracket requires 11 1/4" balls per side. Throw away the carrier that only used 9. More balls is good.

Sounds like you need to find a shop with competent mechanics.

Thank you both for your replies. The spindle is indeed 131 mm without the threads. Just for fun, I measured it again and with them it hits a whopping 156 mm length!

The longest BB that I managed to scrape up is a VP components with a 127.5 mm long spindle. I eventually bought it and installed it today, and it fits quite well too, actually the left crank still has plenty of space around. This round of renewal & repairs is still unfinished so I only had the chance to try the bike out for a few meters... I'm keeping my fingers crossed.

On a sidenote it occurred to me I just assumed the lower quality BBs have 9 balls when instead mine only had 7. Talk about cheap! as I said in my other thread, this is a 20 yo road bike but still..?

PS: removing the right cup was an adventure in itself, kudos to the late Sheldon Brown for his wonderful site and all the people who are keeping it alive.
PPS: most of the shops in my area are small and seem to be one of two types: in the first one the owner also does repairs and is seemingly always busy fixing an old bike in for trivial repairs. The other is more upmarket, and the owner appears to be constantly intent on selling an expensive bike or two. Either way they don't seem to be interested in wasting too much time with me, and I ended up buying most parts in a chain store.