SOS! A Diff seal four-mortar Golf 1,6 D 1980

Hi. I have Golf 1,6 Diesel engine 1980 (four-mortar) has started to sweat an Diff seal -VAG 020 498 085.  Under the catalogue like have brought new, the master has not checked up before to dismantle - as a result a seal does not suit. Have started to search already more attentively and - here where the main ambush - it IN GENERAL have ceased to release. What to do?
Probably I badly searched? :dontknow: