I have a 98 Buick Century that I need to replace the tranny. The number on the tranny tag is a 618AHW. The number on the tranny I want to use is a 619AHW out of a 99 Buick Century. Salvage yard cross reference says these are interchangable. One gm dealer told me these are the same gear ratio and will interchange and another gm dealer told me they are different gear ratios and won't interchange. Who can tell me or who can I call to find out for sure if it will work?