Considering buying a D4 7U for work (not show); it needs to earn it's keep!!

Apart from oil leaks, what should I look for? The grouser bars look well
worn, but the seller says there is plenty of adjustment left on the track
tensioners, suggesting good pins & bushes. Pony engine has electric start
via a V belt from the starter mounted on the left hand guard.

No indication of operating hours.

A Drott tool bar has been fitted with 7 substantial ripper tynes, but it
is not clear in the pics how the bar is fitted to the tractor frame. I'm wondering if the tractor is capable of using 7 tynes.

TIA for any pointers.