What do I say to the boss if the truck is unsafe?

Hey guys, i've been driving for about a year now. I've got a class A with all my endorsements (no hazmat). I started out driving for a company that hauls petroleum coke out of refineries. It was a nice, new outfit with about 40 daycabs. All their trailers are 40ft end dumps. I've got a lawn business on the side and had to quit because they wouldn't work with me on cutting my hours down, etc. So I went to work for a local concrete plant that has 5 mixers and 3 end dumps. The mixer i've been running had some tranny problems (wouldn't go into it's high side) and is in the shop, so today they had me run one of the others that has been sitting. This truck leaks oil like a siv and rocks side to side really bad when it's loaded going down the road. The brakes aren't that great either and the dash falls down into the floor (sometimes keeping you from shifting). They want me to batch in the morning at 5am because they've got some big pour lined up and need all the trucks going. What should I say to them? I really feel like the truck is unsafe to drive and it could cause an accident by the way it rock side to side and it's hard to keep it in my lane. I don't want to cause a scene, but there's no way i'm going to drive this thing. It would be totally unproffessional of me to do.