kick start, electric start problem

i was going to sell my 00 501 e to purchase a leftover 05 mod my dealer had , after sleepless nights ( due to how much $$ i have in the bike and what i could get for it ). i have decided to keep it . rode it over the weekend and my battery needs replacement . it has for a few months now , no worries i've just been using the kick starter , starts first or 2nd kick every time . but when i was out in the middle of no-where , i went to kick it and the electric starter motor was engaging with the kick starter . i rolled it down a hill pulled the decomp in and luckily it started . rode back to my truck and it kicked fine . took it home and it was engaging the electric start motor again .doesnt do it all the time . i have made the comitment to replace the battery this week , but never had this happen before i have owned the bike for 2 years and never had an issue . i was told that the cases had to be split and the sprag gear needed to be replaced at about 400.00 for the parts . has anyone had this issue , and does the repair cost sound rite . ive had the motor apart ( topend rebuild , etc ) but never had to split the cases . thank you in advance for the replies ...