I am a tin guy out of old habits, but I will say one thing, I don't think they do much anymore other than maintain decent geometry as a shim
When they were designed you had umbrella seals, GM had o-rings, and you had to avoid pooling and keep oil away from the valve seal. If the guide was bathed, the seal did nothing
Today, it may direct a little bit back, but I will say once you crush the ends for end stands, it likely doesn't do as much. That being said, even if they were incredibly effective, they do little to force more oil to the mains and cam. By restricting and using a modern valve seal, the rest of the engine gets a bit more oil, and in the end, likely lives a longer life.
I still use them, but now it's primarily for nostalgia and to have a nearly free rocker pedestal shim. I can't see any real requirement for them.