if you are still looking for an MFM drive, i have a seagate ST-251... it currently resides in a 386 machine i put together, but i purchased a 16-bit ISA floppy/IDE controller to put in it instead. this old drive really slows down (as if it wasn't slow enough already) the system when accessing files.
but anyway, as i said it's a Seagate ST-251. 48 MB storage capacity. as far as i can tell, the drive still works flawlessly. i've been using it in that computer for a few months without a single hiccup. i ran a surface scan using ms-dos scandisk earlier today and it turned up zero bad sectors.
the thing is, your 5150 only has 8-bit ISA slots and the MFM controller card i am using is a 16-bit full length card so you would have to locate an 8-bit card elsewhere to use it in your XT.
just for kicks, i tried putting that 16-bit card in an old 8088 motherboard i have and of course, as expected it was unable to access any data from the drive.
what i REALLY need to get my hands on is an 8-bit ISA floppy controller and/or IDE controller so that i can finally get some use out of my 8088. i've been wanting to play some oldschool games on it like Janitor Joe (aka Jump Joe) and some others... i tried running jump joe on my 286 with the turbo turned off so it ran at 5 Mhz, and it was STILL way too fast to play at all, lol.
i also would love to use my 8088 to run the DOS IRC client software i wrote in quickbasic... (using interrupt calls to the waterloo dos tcp stack TSR... that was fun to write
)
anyway, if you are interested let me know. if you happen to have an 8-bit floppy and/or IDE controller card that my XT could use i would be very very interested in a trade.