Back in 2002 I paid the princely sum of $2100 ($1500 USD) for a 1998 Hyundai Excel for the wife, who was sick of driving my Ford station wagon, and wanted something small. The Hyundai was cheap because it wasn't well looked after, the lady I bought it from was very economical with servicing, so it only had 2 oil changes in 60,000 miles!
When I lifted the oil cap the sludge in the rocker cover looked like Davez pics, so I did a couple of oil changes and used some engine flush etc, and while it ran like a timex watch, it also ticked like one, due to crap in the hydraulic lifters. Being a cheap baastard, I always just put up with it, and to be fair, that little car has been fantastic, we've driven the wheels off the thing over the last 16 years, and it's still running fine.
Last year we somehow ran it right out of oil (I suspect that when my son did an oil and filter change, he dropped the old oil but forgot to put any fresh oil back in it) and once I'd put 4 litres of oil back in a few months later, it continued to run fine. About that time I tipped half a bottle of Seafoam into it, and after a day or two (or maybe a week or two, I don't drive it much) I noticed that the "Tick" had gone? Amazing! My wife has a newer Hyundai now, but refuses to let me get rid of the (now 20 year old) Excel, even though most of the clear coat has fallen off and it looks like schidt. Also, most of that burned on sludge in the rocker cover has disappeared too. I think I love Seafoam..........