Interesting purchase...

Very new to the forums and appreciate any advice I may receive. My much loved, 1988 Toyota Camry has driven its last mile and must be decommissioned. After weeks of looking, very, very thoroughly at every possible purchase within my budget of (a very low, 2,000k) I've found a 2004 Ford Taurus Se. The cosmetic condition of this car is absolutly flawless, interior as well. The car shifts smooth (an automatic), rides very well, no knocking, ticking, bumping or noises of any kind but the hum of a well cared for engine. The seller is asking 2,800, which I can swing but only if I must. The transmission, the seller tells me went out around 100,000 miles and was immediately replaced with a new transmission. The distributor hit the bricks several years ago, and like the transmission, replaced. The only thing holding me back from buying the car is that the engine light is on. He says he brought it in for diagnostics but nothing came up. We're taking in again tomorrow to hook it up to the diagnostic machine one more time. The engine, seems to be running fine, is low a quart of oil. I asked where the quart went, he explained he hasn't really checked it in 8 months, and it doesn't leak or burn oil. The oil itself was dirty, it needs an oil change. I'm looking for reliability balanced with space, and near my budget its the first car that hasn't seemed dropped from a cliff, stolen (I actually had a guy try to sell me a car he didn't actually own), or a very questionable transmission.

What I'm looking for is,

1. Questions I should ask the mechanic when he runs the diagnostics, and puts it up on the rack for inspection.
2. Any advice anyone here may have about known issues with this specific make and model.