Here are some pictures of Beche hammers
If it´s a beche hammer, i think its a ( L3 Peter )
As you se in the picture there must be at least 15-20mm ( with the hammerhead and the dies installed) space under the piston to the air inlet from the valve, otherwise the hammer will run uncorrect.
If you let the hammer run for it self, and not to touch the handlebar,for about, lets say 10 minutes, i think the oil should stop leaking som much.
If it´s still leaking after that i think you have to slow down the lubricatoin on the lube pump, but be wery shure not to put it down to much, because that will damage the hammer soon.
Is it an automatic lube pump or is it a handpump?
If its an automatic pump, you have to adjust the pump so it comes a
rop of oil ewery 30seconds.
Hope that will help you Vallentin
Look in the gallery for bigger picture
Roger