For some inexplicable reason, Triumph did not fit valve stem oil seals, relying instead on a very close tolerance between valve and guide to prevent excess oil loss. We have recently found valve stem oil seals that can be fitted to a range of our engines and have found them to be extremely effective in controlling the flow of oil down the valve stem (see pt no. HR631 Note this is not suitable for all engines)
If the guides are in good condition and you are not using one of these external oil feed pipes, then guide seals won't make much difference to the oil consumption. What they may do is stop carbon deposits building up on the back of the inlet valve and spoiling the airflow into the engine.
On an engine with single valve springs you can use the seals from a Ford SOHC Pinto engine. They are a tight fit, but they do fit. On engines with double valve springs the top of the guid needs to be machined down to take a smaller seal - as Mattius says thw VW golf/polo seal then does the business.
You only really need to worry about the inlet valves as oil is sucked down the them by the manifold vacuum. The exhaust pressure tends to push oil back up the exhaust valves and any oil deposits forming on the back of the valve will soon be burnt off once you give it some stick!
Nick on Sideways-Technologies Forum