It seems that I am one of the experts, but I will freely admit that excavators are not my forte.
I was hoping one of the other forum regulars who is more into excavators would chime in to your thread. Their silence leads me to believe that you're fresh out of luck. I looked in the Cat system everywhere I could think of and found a grand total of zip.
My last chance in the Cat world is an email to someone I know. Maybe he can come up with something.
Posted below is the main source of cross-reference information for Japanese-built excavators. If you refer to
whatsapp backup Table 4 you will note your 7DK-prefix machine is not even mentioned, the list skips straight from 311 to 315.
Another thought. These guys sell Service Manuals for Cat machines but they do not list one for 7DK. However if you contact them direct using the link on the page they may be able to come up with something.