Help Diagnosing Clutch Master/Slave Cylinder

[SeismicPumpkin]

'88 325is
Over the weekend my clutch pedal began only returning halfway. I was able to engage the clutch still and drive it home. Yesterday I went to move it in my driveway and it was harder to get into gear. I've yet to get under that car but looking at the master cylinder it looks like there's some corrosion on the outside which is making me wonder if it's developed a leak and letting air into the line. I ran the vin on RealOEM to check the diagram and it shows a separate reservoir for my clutch master cylinder, but when I check under the hood it's got a soft line running off the brake reservoir. Should I replace the master and slave cylinders together or just the master? Also, does anyone have the part number for the soft line with the fittings? I want to compare it to the one I found on RealOEM. Thanks!

[reelizmpro]

That has seen better days and is probably original. Replace it with a good known brand like OE BMW or FTE. People have been complaining about Febi cylinders failing so steer clear of those. Run new clutch line from the cylinder to the brake reservoir. They sell it in bulk also. The new master should have the plastic elbow fitting on it but if it doesn't, get a new one...do not resuse the old one. I think the separate clutch fluid reservoir is mainly for right hand drive models. Certainly not necessary if the brake fluid reservoir is there and has a nipple for the clutch master. It's recommended to change the clutch master and slave at the same time but not necessary. It makes sense to do both at the same time though.

[Panici]

Definitely do master/line/slave as a set.

If one is failing now, the others aren't far behind and you'll be messing with and re-bleeding the system each time.
Learned this one the hard way.

There are aftermarket kits that will replace the hose + hard line with a single hose, if you so desire. It's a good option if your hard line is corroded, so you won't have to custom bend and flair a new piece of hard line.

[TobyB]

I see some external corrosion....

So the pedal's not returning. This isn't usually a hydraulic problem, sorry to say. How's the funky spring on the clutch pedal doing?

If you're lucky, it's corrosion/wear in the pedal pivot, inside the main cylinder, or the pivot at the main cylinder pushrod. Or binding in the secondary cylinder itself.
If you're unlucky, it's wear/binding at the throwout bearing sleeve, a shot diaphragm spring in the pressure plate, or a fragmenting friction disc (unlikely)

Diagnosis, step one. Jack up car, get clutch to stick halfway down, and crack open the clutch bleeder on the secondary cylinder.
If fluid shoots out, then the main cylinder's holding pressure in the system, and you can eliminate the secondary cylinder and
focus on everything up- tube of it. Including the tube, incidentally, which may be corroded or internally collapsing.

If fluid dribbles out leisurely, then the binding's either inside the bellhousing or in the secondary. loosen the nuts, and see if the secondary
gets shoved out of the bellhousing. If it does, winner, the secondary's probably binding internally, and you can swap and bleed it.

If not, sorry, trans out time.

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or some similar variation on that theme.