Squirt a little penetrating oil on the retainer/keeper assembly and give the retainer a medium-firm tap with a ballpeen hammer before compressing the spring. Is the head on or off the engine? If you're doing the seal change with the head on, be sure the piston is at TDC or close to it to avoid dropping the valve into the cylinder. Once the retainer is compressed, use an awl or an ice pick to pry the keepers out of the groove. Sometimes they stick pretty tight.

If there's any noticeable wobble of the valve in the guide from wear, an umbrella seal will get you a few more miles before it's time to replace the guides. If the guide is snug, use the original O ring seal. Too much sealing will cause guide wear due to lack of lubrication.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!