I don't have any ‘major’ problems: I'm about to buy a used DC-618 (public auction), so I'd like to know the procedure for accessing the machine's counters (on the DC 615 and 616, all you had to do was turn on the machine by pressing the two job buttons simultaneously and then typing 02 to access the counters), but since the 618 has a fairly different interface from its two predecessors, I assume the procedure has changed.
And I always like to have the service manual for a machine I buy second-hand because I figure it will come in handy sooner or later.