Completely agree with genIIIbandit and hako on this. Had a VS SII wagon (at 132km) decide to start slipping in 4th going up a 20 degree rise towing a trailer with a load on. She had been doing 80km/h and all of a sudden started slowing and the revs went north. Trans fluid spewed out the rear of the car and coated the floorpan under the driver's seat and back. There is certainly a breather near the top on the driver's side of the box and this is where it all came from. She had a trans cooler as well, but the oil ponged when I checked the level. Basically after about 5 mins on the side of the road, she'd cooled down enough to drive home and it didn't do it again from that point until I took it in to get the box serviced about a week later. The box shop ran the tester thingy and checked the computer was definitely trying to engage all gears (including lockup) and found the lockup gear was not doing it's bit either. I got them to pull the box, replace the torque converter, check / replace the frictions and oilpump, upgrade the lockup valve, flush the system and cooler and replace the filter. Gear 3/4 frictions were about half worn (so did them anyway), but the main forward drive unit was worn out. The oil pump was completely shagged and the torque converter was blue from heat exhaustion. The external cooler was clear, but the filter was full of crap. Basically the guys reckoned that the filter starving the system was the cause of most of the wear, so I guess it certainly shows you that regular maintenance is a necessary evil!!! I blame the last owner....... Definitely get a service on the beast before she does the full monty!