Thats definetly not right. Either they got a defective speed sensor (which is not that un-common in the parts world)Or they messed something up. Its DEFINETLY on them to fix it. Specially if you didnt have that problem before. They are COMPLETLEY obligated to make it right or give you your money back.
Think about it like this. You paid someone to perform a service (in this case for you its non-sexual), they performed said service and didnt live up to what they said they were gonna do. You still have leaks (granted which may or may not be the same sensor) But now you developed a new problem that could ultimatly cause more issues.
If I were you, Id take my car there tomorrow morning, drop it off and tell them, dont call me till you fix it. And when I come to pick it up, I wont be paying for anything!!
If they give you ANY shit what so ever, you tell them that the Bureau of Automotive Repair will be notified and they will handle the situation for you.
The Bureau of Automotive Repair is like the better business bureau for the automotive world. This is ALL these guys do is regulate this kind of thing. They are a government controled agency that literally has the power to walk into ANY shop and completly shut it down. They can fine the shop tons of money and is really bad for them. check em out here
http://www.autorepair.ca.gov/. I suggest calling them to get a ball rolling if needed. They dont wait no 4 to 6 weeks type shit, they jump on it right away!!
But give the shop at least one more chance to fix thier mistake. Id be interested in knowing what they are telling you as far as why they cant fix it. and why do they insist on giving it back to you still fucked up!!