The actual amount of diesel taken to the Ross Revenge by the Galexy in 1989 was in the region of 22 tons, which was about enough to keep the station on air for two months while only one relatively low power transmitter was being run.
Captain Alex only did two or three runs, and later supply runs only delivered about 10 tons a time.
There were still quite substantial reserves of fuel onboard the Ross Revenge at the time, so it was spring 1990 before the station started having to close due to no fuel tender.