I recently bought this welder untested for £25. I rigged up a temporary lead & luckily it was welding ok. The paintwork wasn't great, particularly the top. Cleaned up with a knotted cup wire brush & the angle grinder. I decided to check if there was any crud in the tank. Oil was spotless, cleanest one I've ever seen. Here are some pics of the internal workings of an oil cooled welder. It's no wonder these get scrapped - there's a lot of copper in there!