This HDX900 was very well maintained by Paul Celona at Macie Video Services. I was always able to have the cost of the service paid for by the production is was on so it was serviced between every season.
I just tested it using a blank DVC Pro Tape and it records and plays back fine. No issues with the SDI port. I cannot find anywhere online that shows how to check the hours, but we've had the heads and recording head replaced whenever it showed signs of wear.
The viewfinder is a Panasonic AJ-HVP20P which also works with no issue.
Please let me know if you have any questions.