Defender, Discovery, Motorhome – Before n After rustproofing

Classification: d) Very rusty vehicles where I either find one instance of rot or where no rot is found but it is expected that the customer will have to bring back the vehicle for re-treatment at least once under the guarantee. These customers will have to pay an extra £100 for the guarantee and £200 for re-treatment under the guarantee.
I drilled into the door post of the bulkhead on the passenger's side and found I was drilling into filler. There is also some rot visible higher up. (See picture) I was unable to insert the probe properly to inject as there seemed to be an obstruction. I angled the probe and injected but I can't be sure if this reached the bulkhead. I couldn't tell whether this was just a minor cosmetic repair or something more serious.