A LATE rally in property counters helped the Hang Seng Index to vault 10,000 yesterday and finish 1995 at its year high. The index closed 75.22 points up at 10,073.39 after ending the morning virtually unchanged. Turnover was a sluggish $2.59 billion. The market had left everybody guessing whether it would finish the year over 10,000, but an announcement that the Government had extended the pre-sale period for uncompleted flats brought out the buyers in the afternoon. The top property developers led the last day's trading. The market was also boosted by an element of traditional end-of-year window dressing, with some investors looking to balance their books by picking up cheap stocks. Brokers see the prospect for lower interest rates helping the market to extend its gains next week.