2003 Turbo Conv, what to look for before purchase?

Ok, I totally understand. I'll revise my list.

1. A thorough LONG test drive that goes through all temps, and uses all gears many times, as well as top gear highway cruising. Watch for any slipping, and watch the tach carefully on the highway. It should be dead steady, not moving 1-200 RPM as the trans slips.
2. While doing #1, plug in a bluetooth dongle to the OBD2 port, and run the Torque App on your Android phone/tablet. This will allow you to data log your drive. You can also check for codes (and historic codes).
3. Ask for the receipt for the most recent timing belt service. They won't have it, so budget an additional IMMEDIATE $250 (if you DIY)/ $900-1k (if you pay) to have the work done. You CAN NOT put this off.
4. Get the car up in the air, and have it inspected well. Things like rotors, brake pads, exhaust (especially the stupid short flex pipe), tie rods, ball joints, rear suspension bushings, rear shocks are all getting to the age that they will need replacing.
5. Make sure that it has the correct PINK G12 coolant in it! Green or brown is bad.
6. Call VW dealer with the VIN of the car, there have been multiple recalls for the 1.8T for coil packs.
7. When the timing belt is being done, drop the pan from the trans to drain the fluid, change the filter, and refill with the expensive fluid (or something compatible). Use the correct fill procedure, there is no dipstick. VW will tell you it's a "lifetime fill". They will also tell you it's $4000 for a new transmission. Change the fluid, and you might just get another 75k out of it.
8. Also while it's up in the air, inspect carefully for coolant leaks. The coolant will leave light pink crusties. Common leaks are the AUX water pump, and the metal coolant pipe that runs along the passenger frame rail.
9. Take the top off the aux fuse box on top of the battery. Inspect carefully for melting/scorching. Pull the green fuses to look for charring.
10. When you do the timing service, put in a new thermostat and coolant temp sender. Don't skip this.
11. Put in the updated Diverter Valve. The old one goes bad, and won't throw a code until the car is driven hard.
12. Do new plugs when you do the timing belt.
13. The soft touch gunk on the dash etc will get disgusting.

That's it off the top of my head. Just honest advice from someone who has taken care of a 1.8T NB for a decade (and a little time with a TDI Jetta that happens to be auto).

If you have more questions, lmk. I'm sure I've forgotten something.

14. All the usual stuff of any used car purchase. All bulbs, accessories, AC, heat, windows, cruise, sunroof, radio, heated seats,turn signals (controlled by the hazzard switch which frequently fails) etc etc
15. Print out a pic (or, on your phone) of what lights are supposed to come on when you turn the key. Make sure they all come on
16. Lift up the trunk floor cover and look for the jack/tool/spare tire/wheel bolt lock.
17. TWO remotes that both work.
18. Check the locks on both doors, and, test the key in driver's door lock functions.
19. Confirm the dipstick tube isn't broken. It will, eventually.
20. Ask for receipts for oil changes. It is important that 5w40 of the proper spec was used in the 1.8T. Also important is if they used the oversized Passat-style filter that allows more oil to be used.
21. When it's up in the air, make sure all the side skirts and skid plate is installed under/beside the engine.
22. Check the exhaust coupler in the middle of the car. They rust out. Replace with the OEM part, not cheap pipe/clamps.

I'll think of more...

Budget about $900 for a valve body replacement/rebuild if you can DIY, this car is right at the point the valve body starts to take a dive.

As mentioned, timing belt, water pump and thermostat are important.

Oil pick up may be partially or soon to be clogged if the engine is running cold which it WILL be.

Luckly the oil pan removal is easy.

Make SURE the front lower engine cover is on the car. They are aluminum on the convertible and MANY have been removed and left off the car, you NEED this on the car. A replacement is hard to find used, I think a new one is around $350??

Check the passenger side inner CV boot, it will likely be broken and throwing grease.

Door latches, these go bad and cause the windows to do crazy things.

Check the rear window for the adhesive coming loose. I thought I was safe, right about year 10 (sometimes earlier in hotter climates), the adhesive lets go, and it goes quickly.

Be ready to babysit this car and do a LOT of DIY.

Seat belt buckets, alternator pulleys, small vacuum check valves.

The valve body removal is not a bad DIY, but it will cost between $500-$700 for a valve body plus fluid and filter.

I am an original owner of a 2003 GLX 1.8t Auto NBC, most failures on ANY car I have ever owned in my life, I have had EVERY problem these cars can have. If the top did not go down, it would have been LONG gone.