If you have a culture setting that uses "," as the decimal separator, you need to use the "INV" variants of all tokens.
E.G.
Set decimal [testDec] value to the converted value of {EXPDECINV: {DECINV:Insurance Excess Value0,0375} * {DECINV:Ship value} }
"{DEC:}" can work coincidentally because a decimal value containing a whole number is rendered as if it's an integer(E.G. 1,0 is rendered as "1"), but unless you're using decimals to only store integers that don't fit in an actual integer value, it's not a substitute for "{DECINV:}".
As Gary suggested already, you can export your profile as a .vap, use a text editor to find and replace "{EXP:" with "{EXPDECINV:" and "{DEC:" with "{DECINV:", then import it again.