If the machine is giving a film jam error but you can find no film in the racks/rollers then you have a faulty sensor either at film entry to the developer tank and/or at the exit from wash/last wet tank to dryer.
How it works is basically one sensor detects the film entering the dev tank and it times the film until it exits the last wet tank and enters the dryer, second sensor. If the timing is more than the time proscribed for normal processing ( I suspect around 8 mins wet and 1.5 min dryer on the D Lab1), it will alarm a jam.
These sensors are there for a reason and if you have a film jam with sensor bypass, you will have a serious problem and possible damage to the processing racks/rollers and not to mention all the customers' films damaged.
Here is a link to the service manual
Locate the sensors and see if you can get a replacement from an electronic store or online. If you can locate them, then buy more than you need. Better to be looking at them than for them.
Let us know how you get on, please.