In recent years, the perforated pipe has been unable to handle flow. I've stuck about 10m of drain rods into the pipe without hitting an obstruction, but it's probably much longer than that.
I'm reluctant to get professionals in, partly because they might want to bring the entire system up to modern standards.
Any ideas on DIY approaches for fixing it? - More drain rods and a camera? - Pressure washer with a jetting attachment? - Dig test holes to inspect the pipe at intervals? There are some trees that I'm suspicious of. - Hire mini digger and put in more perforated pipe to share the load?