"Savo jėgomis" and "a propria cura" do not mean "on their own responsibility". They mean "through their own resources", which implies more than just responsibility, as it implies (for example) that "atsiradusius trūkumus ir gedimus pašalinti", the pardavėjas has to use his own maintenance staff or arrange for contractors to do it. This is what the "savo jėgomis" is about. It means the Seller has to organise it, not the Buyer.

Manau, kad sakinukas turetu skambėti maždaug taip, tik reiktu ji paredaguoti:

Labai patariu paieskoti panasiu fraziu Google, tiesiog atsidaryti Warranty (garantiniu talonu) aprasymu...