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2013 MBZ SL550 with the seats that adjust 3000 ways.
The actuator that moves the seat bottom up and down, the plastic gear at the end of the threaded rod cracked and broke so now the seat doesn’t adjust up or down. Photo link at the bottom.
is there anywhere or anyway to just buy that gear or the threaded rod? I’d prefer not to purchase a $300 seat track for a $1 plastic gear.
if you can remove the gear and check dimensions, there are several aftermarket companies making gears that may be compatible with that mechanism.
Something like this.
eBay has a ton of seat bottoms for the R231, if you can find a cheap one you can part it out. I'm pretty unhappy with the power seats - mine are super sluggish now and make a few unpleasant noises. I'm not sure if the motors are losing their magnetism or something, but sometimes they can barely move the seat up or down.
One further thought -- the damaged gear looks as if it was chewed up by the worm drive screw that engages it. The worm screw was continuing to turn when the plastic gear was at its limit. There should be a limit switch somewhere in the assembly that shuts of power to the motor when the gear reaches it limit. Check for the switch's correct alignment and operation, or a replacement gear will meet the same fate.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Good luck! A new seat bottom from the dealer will be around $2400 plus labor. That includes the complete frame assembly with motor, but not the cushion. NEVER put anything on the floor behind the seat. Something like a water bottle will break the plastic part that holds the motor.
eBay is going to be the way here...
Hard to find service parts is one of the reasons I love eBay so much
Unfortunately, eBay doesn't seem to have any R231 seat rails listed at the moment. Plenty of bottom cushions, without the tilt/lift mechanism and rail. I do see them pop up though.
Seat (plastic) gear stripping is a fairly common issue though. So much so, that companies make aftermarket gears for MB (and other manufacturers) seats. I've had to replace several over the years, including my R129. I would try for a metal replacement if you can find one, and have the patience Usually can find them on Aliexpress, Amazon or eBay. It will be much easier just to swap out the whole part for a used one from the wreckers or eBay though. As @JettaRed mentioned, never put anything behind the seats!
I would run adaptation on the seats after replacing the motor.
Not to get too sideways but, speaking of eBay scores, there are some nice R231 parts starting to show up.
It wasn't something I was really looking for, but was so ridiculously cheap, I couldn't resist...
Hey Keon. I have the same problem with my R231 2013 SL63 and have been looking for the seat bottom (adjuster) forever and have not found any on ebay or anywhere else. Am I not using the right search phrase?.
I brought my 2013 SL550 in my indy to have my dynamic seats looked at. In the process of diagnosing the issue, there is a plastic part on the seat that controls the height adjustment that was found to be broken. The "fix" was to replace the seat frame to the tune of $3,700 for the part only. Seems ridiculous to spend that amount of money to replace a $10 plastic part. Not sure if it is an issue with the gear or the housing that holds the gear - I suspect it is the housing, but I need to confirm with my indy. Has anyone found a good source for these types of parts? Looking through eBay, but I'm not really sure what description I need to input as this isn't a part Mercedes sells apart from the seat frame. Always up for the challenge to make the fix, but need to find the part. May need to find a donor seat...not sure if seats for the R231 share parts with other Mercedes models.
If anyone else has successfully fixed this issue or has a source for such parts you can recommend, I would be all ears.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
The seat frame should be closer to $2400, not $3700. Still, outrageous!
I had the gear that controls the forward and back movement break and it was probably close to $3000 at the dealer to fix. But I have a vehicle service contract (VSC) (a.k.a. 3rd party warranty) and it cost me $100. However, it was a pain in the butt and a month to get the VSC company to approve the repair.
Always up for the challenge to make the fix, but need to find the part. May need to find a donor seat...not sure if seats for the R231 share parts with other Mercedes models.
Only way to find a compatible part, is going to be to get the defective part in hand, and take/compare measurements. I suspect the motor or some of its parts are probably shared by multiple MB vehicles.
There are many companies that make gears for robotics, etc., such as https://khkgears.net/new/plastic_gears.html
You need to know the specs on the gear you have -- diameter, teeth, pitch, shaft diameter, etc.
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Usually can find them on Aliexpress, Amazon or eBay. It will be much easier just to swap out the whole part for a used one from the wreckers or eBay though. As @JettaRed mentioned, never put anything behind the seats! 
