Why is business dying?
local economy? lose a good service advisor? increased competition?
retention systems do work well but if the " cancer" is internal they tend to emphasise the acuity of the problem...
as for marketing ideas my favourites are the following:-
1) Pick 3 or 4 of the largest local employers and develop an employees benefit plan and pitch it to the owners - we give 10% off parts and labor for working at their business, $750 in free accessories at time of vehicle purchase and a $200 parts/service gift certificate for every 5 years of service to THEIR company (year 10 get 400 bucks etc etc). penetration is awesome, staff are well paid and love the service and the word of mouth doubles the potential... it is great.
2 - inactive mailers with well thought out incentives ... go colour and postcards everytime.
3 - community support events - we donate a "beauty and the beater" car every year for raffle - proceeds to womens shelter/kids charity. we take a sub $2500 trade in and get all our vendors to help out... we fix it, the body shop paints it, tire shop does rims and rubber, stereo...etc etc you get the idea. Then we sell tickets for a raffle to be held at the store. local media love it as it is a great story - charity get behind selling tickets, good karma from helping the cause and really, it is a big gesture for not a ton of cash.... ancilliary benefit is the tech slove it too... big softies that they are...!
you sdaid crazy ideas so there you go ok??

Good luck.