hey feral, im adduming you are referring to the bowl that the platic floats are sitting in, on the top of the carby.

that bowl is where the fuel sits before being drawn into the engine.

these cars are not rising rate like the SU's and therefore DO NOT take oil in that bowl, it comes directly from the fuel pump, then is drawn in the BOTTOM of the main jets, and is balanced with air from the top (air corrector) and is fed into the air-stream via the auxiliary venturi

other than lubircating the main throttle shaft, there is no oiling system inside a weber or dellorto carb

Edit: just thought id add that SU's have a fixed air/fuel mix based on the depression formed behind the damper, by regulating the damper rate of change (using oil), variations are smoothed. When i had an SU, i used auto-tranny fluid, and a rich needle.