Good Morning, I bought a car, Mercedes Benz SLK for £2,900

Good Morning, I bought a car, Mercedes Benz SLK for £2,900 from a dealer in Fleetwood in February. Since then I have driven 86 miles in it and 66 of those miles were bringing it home from Fleetwood. The rest of the miles driven have been to various garages and back. The passenger side of the car flooded a few days after getting it home and the windscreen wipers failed. The dealer paid for the repair but the SRS warning light kept flashing on and my local garage didn't have the necessary technology to do a diagnostic test. On my way to a garage that did, the car ground to a halt and had to be rescued by the AA. The alternator had failed. The dealer duly paid for another alternator, second hand I may add, as was the wiper motor. The garage identified a few more faults such as cracked tyres and a rusty torsion bar which the dealer refused to put right. The garage was hoping the replacement alternator would cure the SRS warning light but on my way home it came on again so I returned to the garage. The diagnostic showed that the SRS unit needed replacing. That was a month ago and I am still waiting. The dealer will not pay for a new unit, he says he is trying to find a second hand one. I have had enough and would like my money back but the dealer refuses. I think three months without the car and no courtesy car provided is long enough. Please can you advise me where I stand.
Regards,
LB