Walther Cp88 not indexing

[evert]

Leak is definitely from the valve itself? (not just the seal twixt capsule and valve?). If you are going to strip the valve itself, best off changing all the rings, not just where you think it leaked from. The thinnest (really virtually none at all) of smears of silicone grease on the seals before reassembling can help.

Took the gun apart again, and the O-ring around the valve exhaust stem was visibly damaged, which corresponds clearly with the leak I experienced.

Some years ago, I was given a wreck of a Umarex 586. It contained the same valve as the CP88, so I had another of these O-rings.
Changed it, careful not to damage any seals, and the gun now seals well, indexes and shoots, so success getting it to work.

Now the net problem arises it shoots way too high!
The rear sight is windage adjustable, but theres no height adjustment.
Are there different front blades for these?