You guys are way too harsh on board participants for whom English is not a native language. This is the internet, we have readers and participants from everywhere! I help moderate a Cessna 150 Club forum and we have participants from all over the world. The Aussies and the New Zealanders are difficult enough to understand (grinning) but the guys from Philippines and Spain is darn difficult to figure out, but we take the time to do it, as his question might be critical to his safety. Dang, Georgia Redneck is tough enough to figure out!
Tokimo, If your travel agency has only two or three vehicles in general use, with no unusual driving, you really don't have a fleet maintenance issue. If you have six or eight cars or minivans and are, so to speak, "running the wheels off them", yes, you need to establish some procedures and policies on the maintenance of your fleet, mileage intervals for oil changes, etc. type/brand of tires to use, and other items. Your owners manuals for most cars specifies maintenance intervals for normal operation, and for heavy duty use. Normal driving, even in a city is not heavy duty use, but these maintenance schedules will help you alot.
Set up a erasable marker board on your office wall. Each line is a specific car or van, each column is a maintenance item, such as oil change, air filter change, etc. and also have a column for current mileage and date. About once a week read the mileage on each vehicle and write it down. If you get this board set up right (or if you are good at computer spreadsheets, do it in your computer) you will not overrun any maintenance on a car. If you set up the spread sheet, you can put in the required intervals and set it to flash when you get close or over. Once or twice a week, enter the mileage and see what is coming up next.