Oven burner only partially lights

[plainsman]

Have had problems with the oven burner not lighting all the way down the burner strip, as if the gas wants to blow itself out. I had similar probs with the hob incl an occasional yellow flame but cleaning the jet solved this. The bit of flame on the oven that is lit burns blue. I have cleaned the oven burner best I can and cleared the injector with a bristle. There is now less of the burner lit up. Thought it may be the regulator - its the manual change over type. When I released the joint a load of oily gunge came out. It had a slight yellow colour and stank. Some oil/gunge in the pipe after the regulator but nothing in the flexi between bottle and regulator

 

Can anyone help/advise please?