For how long do you or have you used the Scania S for?
I have a theory....if your Scania S has the most miles (as in distance covered) on it. Then I can only suggest that you use your new FH5 and pass the amount of miles you have on your Scania S.
(I have 2.2 million miles on my old Volvo FH4 and started using the FH6 as soon as it came out and I only have 131.000 miles covered on it so far within the 3-ish months it's been out.
TLDR: How many miles does your old truck have on it and how many miles does your new truck have on it?