We have a Biggs & Stratton Yard Man lawnmower about 7 years old. We have always had it serviced but now want to service it ourselves. I can't find our manual for this lawnmower. Please can you advise. We have tried looking this up on your site but can't find our model number etc. This is as follows... YARD MAN XTL55 18 INCH. MODEL: 409B. PRODUCT CODE 036102. FULL MODEL NUMBER: 11B 409B 671A thank you for your help