by a service kit that are made for your model
I do you a suggestion how you can do it yourself if you have a burner to heat up the bolts because of loctite sealant i think you know something of forces on that parts ? because of the tools that are neccesary to service it .
Here is a suggestion of a brand that is maybe there or coming in your Country . thats why i do this suggestion by a dutch link .
If you know the brand of your hammer ? sometimes bought secondhand and no modelname google it on 3 words powertools the brand service or choose pictures if you will see pictures where you can see your hammer but there are can be marketing technical differences by the models because a suggestion i made by Hitachi the H90 and H90SE are not compatible by service kit a part of spares can only be used.
The time you spend is meaningless if you only think its leaking oil. because there is a thin lubrication inside most jackhammers and if that's leaking ,the working hours are on it, for time wasted re prematurely burned grommets make high-priority work bolt seal the front of the machine at the stroke chisel the first rings oil seals as well as the size of the stroke bolt must be tight and smooth, as if only a little air leaks burned den all your new o-rings (ie be hard in the short term) by overheating, use lubricants, not just fat because of the high temperature internal structure and the thermal conductivity of the parts together.