buying used car and my rights please read and help asap..

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any help would be wonderful heres the story. I have not so great credit becasue i havent ever gotten a lone in my life finally i get the score up high enough for a car lone of about 11k with pretty high intrest but im willing to do this to better my life and credit if i get a nice car.. so heres what happened so far.. I went to a used car dealership found the car i wanted with low miles 07 max with 85k miles ..looks pretty nice to the eye and drives like a nice car. prior to buying it i took it to a well known import car mechanic to have it looked at he found an oil leak "probally from the a hose" i didnt pay him except for 1 hour of his time since i was spendng more than i should on the car aready.. he also found that the ac is not very cold the lugnuts on the front wheels were stripped and needed all new bolts and a couple were missing compleatly the (!) light was on he said it is for tire pressure sensor this car has custome wheels and the correct pressure still has the light however.. a few minor things i would consider normal wear and tair a small skuff from bumping parking in sf not a bigdeal im willing to work with that since the car i found out has an extended warranty from nissan on the transmission 120kmiles... that the dealer ship i dont think knows about.. bodys in very nice shape long story short is i came back $100 lighter in the pocket but glad i spent the money... I attempted to buy the car for a lower price so that i can get the repairs done myself from mechanics i know around town.. SOOO>.... the dealership assured me they would repair the ac and he oil leak and the everything else i wrote on the "DUE BILL i insisted on if i agreed they can have the repaired compleated under the terms of the contractual sale.. so i put on the Due bill this exactly "Dealer is obligated to all oil repairs listed in mechanic checklist (the mechanics notes i paid 100 for ...) install compleate set of ceramic break pads for all four wheels change out broken breaklight bulb replace all lugnuts and all lug studs for all four wheels repair AC to normal working condition. fanally My special note i hope helps me... (BUYER RESERVES THE RIGHT TO VERIFY WITH OUTSIDE MECHANIC REGUARDING ACCURATE OEM GRADE REPAIR QUALITY AND NORMAL FUNCTIONALLITY)" they signed it denoted the due bill in the main sale paperwork as well as the mechanics checklist.. in the article to refer to and of course i had a witness to the verble assurance and phisical signing of the documents ... anyway i agreed if they gave me a loner for the couple days so i can continue working "driving around for my biz doing pickups and deliveries" finally after 3 days they called me reporting that its finished so yesterday i returned to the place gave them the rental and took my car. they said it was a powerstearing leak and they repaired it.. they are wrong or lieing im sure of this ive been dealing with old used cars for awhile since i have been in the beater market most of my 28year old life now... so driving the 16 miles back to my home wheels feel like still not all nuts on there kinda feeling ac is very weak however its been recharged they reported.. it does work but its weak for sure...my 97 with 220k miles was nuch better on low than this one on max ac... so the plan for today is what i want advise on Nissan dealership? local mechanic ASE certified well known import guy? nissan wants 140 an hour.. local probally 80-100 work time is prbally im guessing double what nissan predicts so 2 hours for compleate check of all systems.. finally check this out they were hesitant to give me the car since they say the car paperwork needs to be redone but the guy who did the orginal is off and will return tuesday so they wanted me to wait. i convinced them that i will come back and take care of what the hell ever they want then since the man on duty wouldnt do it for me then but with a little sales skills let me take the car .. Mind you i have a bill of sale the yellow carbon copy transfer of vehicle form and approval letter from the lender now what is the best course of action here i feel like i have some kind of hand on this transaction right??