Hurth gearbox

[Mithril]

Hi just joined this site hoping someone can give me any idea on how much oil I should put in my hurth gearbox its a hbw 15-2,5RV not shaw what that means its a v drive box I have tried looking it up " my boat has been layer up for two years " so thought I would check the oil ' when I checked the dipstick it was dry so bought two Ltd of atf destron !!! And put it all in "and still not showing on the dipstick " Ive looked up other models of the hurth but can't find my number on there and the ones I have looked up only seem to take one Ltr which is a worry because I'm wondering wear its going ? Do I keep putting more in until it shows up on the dipstick ???