Reminds me of a time I was car hunting for a friend. I went to go look at this old beat up honda accordian. The thing sounded like it had 2 of 4 cylinders dead. The outside looked ok but you could tell the old hag selling it was a cheap pennypincher and didnt bother mainenence. The thing SHOOK at idle it was so rough. I went to look at the oil and it was SLUDGE. PITCH BLACK GOO. Ever since then, I've been oilchanging every 1000-1200 miles. She horrified me that bad.
Dude!!! Gas costs, what......$25-30 for a tank now? An oilchange costs what....$7 for oil and maybe $3 for a filter. You wont even notice after a while you'll get so good at it. Pull in, slide the pan, pop the plug and go inside. Come back out, put the plug in, pop the front plug and remove the filter while it drains. Replace front plug and fill her up. Get the 4 quart truck oil and you wont even have to hold the oil container. Even a speed oilchange is better than nothing. Drain only the rear sump (practically no oil up front anyways) and leave the filter. Thats a $4 oilchange.
$4 versus (5 tankups at $25 each= $125) It's...for me at least...a no brainer.