Ah I see what you mean. Likewise I wanted to avoid doing any pre-processing because I feel that logstash should be able to manage to process arbitrary input somehow. If it can't then there's something wrong with its design.
My own issue is here:
It seems to me that logstash struggles with anything that isn't a simple predictable log format of
timestamp followed by some data
but even my situation does have that format, just not quite in the way logstash wants it.
Thanks for the info, I'll look into using a cronned sed script or something to preprocess the data.