Valve Seals going bad :/

[EntropiousDesign]

So I recently acquired a '98 Eclipse RS. The car most likely has valve seal issues (The car has 254k on the original 420a). But before I dig in, I like to be well informed. She sporadically smokes (white with a blue-ish tinge) out of the tail pipe, only when idling and generally doesn't matter if shes warmed up or cold. When driving she runs nearly perfect until I idle, for instance at a light or in the drive-thru, and I have to shut the engine off until I can go again. So my main question is, in your guys' and gals' opinions is this the valve seals? It's naturally aspirated so it's not going to be turbo seals or anything of the sort. The timing belt was replace just before the car was bought, so I'm assuming the timing was set right, or hoping more or less.

Also how simple is it to replace the seals if they are the culprit. This is my only car at the moment so if its going to be a multi-day job I'd like to start on a day I have a few days off in a row, so I don't feel rushed.

I'll take some video tomorrow if I can catch her smoking for a visual for you guys

My minor question, as it doesn't seem to be too serious of an issue as of yet, is; First gear sometimes doesn't engage, it's happened twice since I got the car 2 weeks ago. The first time it re-engaged after a few seconds, the second time I just shifted to neutral and back into drive and it engaged no problem. What would most likely be the of this cause this? I'm sure age and wear has a lot to do with it. But if its a solenoid or something going bad I'd like to catch it before it becomes a serious issue.

Thanks in advanced guys!

-Entropy

 

[luv2rallye]

This will give you an idea of what's involved in seal replacement:
http://www.dsmtuners.com/threads/head-on-block-valve-stem-seal-replacement.312891/
http://www.dsmtuners.com/threads/head-on-block-valve-stem-seal-replacement-part-2.313127/

 

[PlanZero]

All of my old 420as had leaky valve stem seals. One of my Tsis has it too but not too bad yet.
I used to just dump some no smoke+ stop leak ($5 at Walmart) in whenever it started smoking and it usually helped. I found this product to work better and cheaper than Lucas. I Used it for about a year before the seals started getting really bad, but conveniently the car was totaled in a collision with a mustang (the DSM came out on top). I realize that this is only temporary, but unless you have the time and/or resources to change the seals, it may help. Just keep an eye on the oil level and do a compression test to rule anything else out.

 

[EntropiousDesign]

I've been pretty weary about stop leak products. Roughly how many miles would you say you could generally get out of using that? And can't it possibly clog lines?