I never take my eggs to the restaurant and ask them to fry them for me. Why? Because if they break the yolks…. it’s MY eggs they broke and I’ll have to replace them. (I learned this the hard way over a $1200 set of aircraft tires which later proved defective. I had to buy addt’l tires AND pay labor Twice…after-all, it wasn’t Their fault I handed them defective tires…nor would it have been Their tires damaged if they installed them improperly.)
When the parts fail…the shop should have to replace the defective parts on their dime not yours.
If the seals you buy fail…the shop will have had no obligation to re-do the job because you supplied the parts.
Tell your hydraulic shop which cylinder model/make you will bring to them and let THEM order the parts…and allow them to have the ordinary mark-up on parts (they likely get a wholesale price anyway.)