Every excavator has multiple hydraulic oil cylinders, and they won't have problems at the same time, unless you don't do the maintenance for a very long time that the oil seal is worn and depressurized. If you find one oil cylinder has problem, especially when it has problem on stretch or contract at a direction or too weak, then you should you should consider that one oil seal might be damaged.

Please be careful not to make the radial direction of the oil cylinder bear force or weld the cylinder, otherwise it will make the cylinder body deform, or the piston and the cylinder body wear.

Remove the oil screw cover at the oil cylinder top and pull out the cylinder plunger and check if the oil sealing is worn or damaged. The common problem is 1: The hydraulic oil too dirty to cause abrasion, and even the excavator is not move, the arm will fall down because of depressurization. The oil seal is damaged because the pressure is too high, in that case, you need to replace a new same model oil seal.

When replace the oil cylinder, clean the sediment in the cylinder tube