How were the Wankel rotarys for working on compared to piston engines back then?
They were easy to work on, but you had to do it much more often. Plus they got crappy mileage. This was also in the era when Honda and Toyota were really getting the piston engines right. My 2003 Honda Accord (V-6) is about to turn six figures and the only non scheduled maintenance item has been an alternator that went bad. I've changed plugs once. Still gets 30 mpg on the highway and everything (Power windows, AC, blowers etc.)still works.
Wankels were a neat idea that just didn't pan out.
Easy enough to work on. Sealing the combustion chamber was a challenge. In a piston engine the only real seal needed is a circumferential seal via rings. Rotary engines require more complicated sealing, namely via an apex seal.
Not really answering your question re servicing, other than pointing out that apex seals require more of it.