Swing check valve maintenance issue

We have received one e-mail from end user that one of our flapper check valve occurs leakage days ago. We also take it as urgent issue. And they have already taken it down from pipeline. Luckily, they still have one another back up valve from us.

End user asked us to support them to disassemble the check valve, and find out the leakage reason. So we send us our maintenance book for end user. We are here to show some important points for the maintenance. Hope it will support some other end user.
The most important thing is to guide end user open the valve. Steps and G.A drawing are as below:
a. loosen item 5 bolts and take out
b. Loosen item 6 screws and take out
c. Fix item 4 valve body, and unscrew item 13 valve cover, then take out item 13
d. Take out item 10. And check whether there is any damage on seal surface of item 7 and item 10.
1. If there is damage, replace item 7 and item 10. And at the same time, replace item 11, item 14 item 15 and item 16.
2. If there is no damage, replace item 11, 14, 15 and 16.
e. Clean each part, and assembly them. It should be used after qualified pressure test.
Pressure test request is as below:
a. Body test (22,500psi)
Charge pressure from inlet, and block outlet with blind plug. Charge pressure from 0 to 22,500 psi, and hold pressure for 5 mins. There should be no leakage or sweat.
b. Hydro static seal test (15,000psi)
Charge pressure from inlet, and block outlet with blind plug. Charge pressure from 0 to 15,000 psi, and hold pressure for 3 mins. There should be no leakage or sweat.
c. Both tests should be implementing twice.

Till the post time, end user informs us there is a little damage on the soft seal item 16 caused to sand. Now we are preparing soft seal and o ring for end user.