I bought a complete reco gasket set for my A15...
When I look at the rubber valve seals they seem to be way too wide at the base to fit the stem.
The valve seal kit also has an 'O' ring for each valve in it - where does that go?
I had a look at a 1200 head and it has the same seals in it and they are just riding up and down with the valve...
The original seals were a metal casing and rubber sprung top that press onto the valve guide.
I can't see how these new kits do any sealing at all???
Has anyone seen these kits and can comment??

The O-ring is an original specification. Sounds like your gasket kit includes two kinds.

The later spec is the positive seal (fits on the guide)

I like the umbrella seals best -- they just fit on the stem, not on the guide.

So the idea is that they act like an umbrella and stop oil from running down the valve???

problem with umbrella is once the valve opens the umbrella goes to the top of stem,then acts as a pump and pushing oil down the valve guide(old school).press on ones don't move and wipe off extra oil.cheers

Are the press on seals available still???

yes, i have in stock approx $30 + postage. pm me. cheers

Umbrella ones don't do that with stock valve train. They shield the valve stem from getting oil in the first place.

Rmove both types after 100,000k, and see which is working better.

For racing where the heads rebuilt regularly either will be fine.

For new heads, Nissan chose to use the positive seal.

I ran into this problem before.

My gasket kit came with umbrella seals and I wanted to use positive type ones so I went to my local engine re conditioner and asked for positive type seals to fit a 12mm stem and 8mm valve (my A12 head specs). 8 bucks later I had some. I used the positive type seals on the inlet so oil doesn't get sucked in under vacuum and the umbrella type ones on the exhaust as the extra oil allows better lubrication and cooling of the exhaust valve.

I used a 12mm socket and a mallet to tap on the new seals to the stem (the fit was really good and will never pop off until you want the reco the head).

Not sure if it helps but my valve stems seals (12mm guide, 8mm stem) were product code K454 - not sure if that helps but it may.