Trying to find a transmission filter for a 63 Pontiac Grand Prix 389 with a 375 Roto-Hydromatic. Every time I go to an auto parts store they give me a flat filter, but the one in mine in a canister. The code on the side of the transmission is PG-63 44721. When the parts guy looks it up and when I look it up online I always see it called a Powerglide transmission. Is there a difference? And does anyone have any suggestions on where I can find the right filter?