Position 856 1617000836 a broken hammer piston in the worst case but you have to order 1 617 000 A15 a maintence kit and special lubrication used 50 ml 1 615 437 512
INSPECT CAREFULLY THE 1 617 000 838 Hammer Pipe for rips if all parts are unmounted of the hammer pipe tap it with a metal object then it should not have any dull sound treat like a tuning fork for control for rips. thats important before repair consideration before.
The lubricant will be quite thick and that can also be the case only , (only have had its working hours on it) the revision of this hammers are easy to do it yourself clean solvent all metal parts that you re-use again to do the job you have a bench-vise and tools , for the striker pin in case there are no special tools neccesary like other hammers like a suggestion the Milwaukee 500S or other proffesional hammer because of the need of special seals and tools are neccesary , in between 1 and 2 hours are taken to service this Bosch hammers sometimes its neccesary to be aware of 1 ring to replace first of all because its easy to forget this ring on position 104 1610210095 o-ring that will very easy forgotten in practise with some grease replace it first of all spare parts.
Bosch Parts Service Online Illustrated Part List