The valve stem seals can be replaced without removing the heads by pressurising the cylinders with the valves in the closed position. this could save considerable money, however the valve guides could be worn and might cause failure of the valve stem seals again , it is a crap shoot. I had the seals replaced on a Mercedes 190E for less than $250 by a very respected german car garage nearby, It quit using oil, but lasted only a year. I then ended up rebuilding the engine. Lower end was fine but the head and the valve guides were bad.