When I rebuilt my transom I also had to attach the stringers in the stern area of the boat. They were no longer attached from the transom to about 3 feet forward. I feel this was due to the flex in the rotted transom. My boat is a 1983 222 CCP! It had a very hard life before I bought it. There are some pictures posted in the Photo Gallery from last summer showing the stringers during my rebuild.
As to how to get access to check the stringers. I could access mine through the deck plates next to the live well. I must admit they seemed fine when I checked them there. It was not until I cut the stern area out of the boat that the problem showed it's ugly self!
If your deck and transom are solid, I would not be concerned about wet foam in the stringers. All it will do is add extra weight to the boat. To remove it you will have to cut the deck out and get involved in a major rebuild!
If you decide to do a rebuild, there are alot of people on this forum that will be glad to give advice! Most of the time it is good advice!