It depends on cost. If they are $ 5 each , then replace all but if $ 25 * 24 =
$ 600 and the car won't go another 200 K then replace the one that is leaking + any that have rapid bleed down when pressure is applied.

Given this is an overhead cam inline 6, lifting a cam isn't that much work. ( This engine is based on the gas M104 from the 90's correct? )