question on stringers

[SkinnyEd]

I'm a novice at his so forgive if I have a stupid question.

I know I have some transom rot and am definitely looking at a replacement job there.

I thought perhaps the stringers would be a problem with rot too but have seen some posts referring to the stringers being of foam and not wood.
Can someone tell me what the composition is for sure and whether the foam stringers are a potential problem area?

My boat is a 1975 20 SF with outboard power.