Hi Andrew416, please note that there is no need to apologize, this is a very interesting questions and one of those topics where if you ask 10 different people the same question, you will get 11 different answers - there are only stupid answers
There are many different stories about peoples experience with oil, and while they may be relevant, more importantly, whether you use synthetic or mineral (without mixing them), and it complies with the Rotax recommendations, you engine will go to TBO if you take care of it.
My experience - I had my 503 go to 745 hours before it was opened for the first time, and I only used Castrol chain saw oil. The reason I used this oil was because, 1) it complies with Rotax specification, and 2) I got it at a very good price - but more importantly, I am a regular flyer, doing in the order of 80 - 120 hours per year, so the engine is used regularly.
I personally saw an opened 503 (30 hours duty, but 5 years old) after it had siezed, and the opinion of the Rotax accredited mechanic was that this siezure was a result of moisture ingress and the resultant corrosion from infrequent use.
Hope this helps