IX Touring Brake issues (MC & Rear discs)

[Wille30]

Yesterday I got in my car and I had the brake fluid light come on and the brakes became spongy. When I do a test I can pump the brakes up for a good pedal feel, but when I apply pressure the pedal will slowly go down. I also cannot find any leaks in the system. So this leads me to think it is the master cylinder. I have read that there are different master cylinders from different car BMW's that work with the IX booster (E32?). Does anyone know what the best option is for a replacement Master Cylinder? is the E32 a direct drop in?

ALSO, I have an IX touring with the ventilated rear discs, but the PO replaced them with standard discs which means my pistons are over extending. I have been waiting 6 months for these and they are still on back order. Is there ANYWHERE that would be a good place to get some discs? Everyone I have talked to says they are on back order. I just don't feel comfortable with the setup that's in there now.

Thanks!

[The Dark Side of Will]

Swap to standard E30 rear calipers?

If the pedal is going down, but the fluid level in the reservoir is not going down, then you have a bad MC.

[mtnbimmer]

Why do you think you need to replace the master cylinder? Why not just replace the seal rings ("rebuild") and call it done?

[Wille30]

well, as it turns out it isn't the MC, its the lines above the rear axle. Which I hear is a fun job....