Do you submerge your scope when brushing

If the scope has been leak tested by manufacturer's reccomendations and passes the leak test- 1-3 minutes in still, clear water, the problem may be the seal on the light guide caps. The integrity of these seals wear down over time. Do you know how old those are? Something to look at.

It should not be necessary to keep an endoscope inflated with the air leak tester in order to prevent water damage while washing it under water. The only instance in which the air leak tester is used in this manner is when you have a detected leak and you wish to put the endoscope through the disinfection process prior to sending it in for repair. The outward pressure exerted from within the endoscope, by the air leak tester, keeps fluid from getting in. In this way, you protect the endoscope that has a leak from getting water damaged. In general, when trying to protect endoscopes through air leak testing, it is important to deflect the tip of the endosope in every direction, while under water, when it is inflated for the air leak test. You could be missing leaks in the bending rubber [most common place for leaks] if you do not follow this protocol. It is also important to remove the entire endoscope from the water PRIOR to deflating it and removing the air leak detector. As Monkeelouise mentioned, you must check the seals to the soaking cap as these can become incompetent over time [dry and crack] leaving the endoscope vulnerable to fluid invasion. I recommend reveiwing the SGNA guidelines on reprocessing of endoscopes as well as the endoscope manufacturer's guidelines. Proper handling of the instruments, along with strict adherence to all the steps of the air leak process [done after EVERY case] should prevent the majority of fluid damage problems. Best of luck.

If you are using Olympus endoscopes then there is someone to help you. Olympus has local personal (Endoscopy Support Specialist) that assist customers in things just like this. Please send me a PM with the account and contact and I may be able to put you in contact with the right person.