Adler 467 Foot Stroke cylinder leaking air

[eerikkarts]

I have an older Adler 467-373 — an excellent machine! All functions work perfectly, and I’ve completed several projects with it already. Overall, there’s nothing to complain about. The entire oiling system works, and the machine is amazingly quiet and smooth.
Previously, the machine received a full service, and all leaks in the pneumatic system were fixed.

However, there is still one thing that bothers me.
When I activate the Max Foot Stroke function, the internal pneumatic cylinder inside the sewing machine starts to hiss. The leak is definitely not coming from the air hose connection but from somewhere inside the cylinder. I’ve watched some YouTube videos, and one machine had a similar hissing sound.

https://www.youtube.com/watch?v=viSc5XD7R2I

My question is: can someone confirm whether this is normal, or is it actually a fault that should be repaired? The leak is not critical, but it does bother me.

[eerikkarts]

I took some time and removed the air cylinder from inside, and now I can answer my own question: yes, the air cylinder is intended to leak air.
The piston seal is not airtight and is made of plastic.

It also looks like the older Adler and the newer Adler Dürkopp 467 models use different air cylinders.

Anyway, case closed!