Here's a past post on that TSB and the decarbon process, I've used Seafoam via the PCV line instead.
http://www.automotiveforums.com/vbul...&highlight=pm2
Here's a post with the detailed instructions on replacing the valve cover:
http://leckemby.net/windstar/windstar01.html
The valve cover is very easy to replace and only runs around $60 and the decarbon products should be <$10 or so. Is there something else being done, if not then definitely do this yourself. The other thing to be aware of is if you do the full TSB it retards your timing to prevent knock resulting in decreased performance and MPG.