stihl 07s oil pump problem

[badfish]

Hello all, I've just acquired a Stihl 07s and its not oiling the chain. I've tried putting diesel in the oil tank for a few days and also made sure the oil feed pipe is clear. I did take the plate with the pump on it off partly and I'm wondering if i could have done something to it? has any one got any suggestions with what could be the problem or how to fix it as parts seem to be a bit thin on the ground.
Many thanks
James

 

[badfish]

anyone?