Example; On a PM list it was written as "gear box needed oil so I filled it" and a work order was passed on to the next shift to repair a leak. Now the planer adds check oil level in all gear boxes, and any other tribulations. Chances are you will eventually find one of these SEW gear boxes. Heck, these rascals have level and fill plug all over it and eventually it will get over filled if don't have the information. Yep, the information is missing from the PM list, what information is there is irrelevant and a PM did more harm then good. It seems to be forgotten that once filled the oil in a gear box it will not magically disappear. Next the gear box is replaced, needlessly repaired and the whole process repeats. Typically, if a problem like this is stopped two more appear because the root cause is not repaired.

Yep, it dun broke. How can you find and fix problems like this? Do you have problems like this and don't know?

I agree that if there is no evidence of a leak you should leave well alone.
The answer to the problem of information is to label the plugs on the boxes with tags or colour codes. Get the SEW manuals off their website and take the time to mark the correct level, filler and drain plugs.
Do you perform oil analysis on these boxes?
Best of luck.