back fous on sony 70-300mm g

i bought used lens sony 70-300mm g lens.  back focus is mostly visible at 70mm f4.5 and f5.0-5.6.

On sony a77 seting micro af adjustment  to -4 everything is perfect. but i have a57

i have warranty paper and no date. in my country ( Slovenia ) they need bill to accept warranty.

first qustion: does this lens have  default  two years warranty? lens were bought avgust 2011.

second q: is is possbile to get warranty from serial number?

third q:  sony wants 250$-300$  to adjust focus. that is a lot of money!!

How much is that in US or Germany or UK?

Are any other solutions to adjust focus?