the FB-354 i think is standard A500 drive. So FB-357 also has 2 little "detection pins?" Problem I had to fix on A500 internal was somehow 1 of the detection pins was off to the side. It was a small delicate job and I used a needle nose pliers but could've used a tweezers to bend it carefully back to being straight enough to go back in. And fortunately it was in far enough and I don't have to replace the drive right now, although I'm sort of scanning for a FB-354 to replace it. If it's like FB-354 then it has 2 not 1 detection pins and if you did everything you could with making sure they have proper action then that's all you can do. Make absolutely sure that the drive reacts accordingly when you push them down though, one at a time, with no disk in. Make sure it spins only when I don't remember if it's one of them down or both, but just make sure of that. If it's not reacting like there's a disk in it when you push them down, then they're not hitting the contacts. I bet you tried this though. But I have to say this because that's how my FB-354 behaved when 1 pin was out of it's path it was twisted to the side so only 1 out of 2 sensor contacts was actually being contacted, and the disk spun spun spun constantly like you say.
