Hi,
I had a similar problem with my OD4, and it developed a pinprick hole in the base, A complete overhaul was needed, a new burner pot was sourced. Kabola says the pot can be removed via the top. that's cobblers, the best way is to remove the fire as the burner pot will only come out from the bottom. It's fairly easy to remove the fire, 2 bolts secure the drip tray from the black round cover. I have attached some pictures showing the burner pot and holes.
I will attach some pictures showing the operation later, a year ago I fitted a new carb. spares for the burner pot and a new mica glass cost about £300, this also included a new cage, carb was £200 on top of that, but I ended up with a virtually new heater.
My fire also provides hot water.