I was thinking of an older pre-2000 Foretravel, but now considering something a little newer with a slide in the 2000-2003 range. Is the ISL motor require more maintenance? Any advice would be greatly appreciated.
Those year ISL engines get better mileage than The M-11 series and don't require any more maintenance other than different belt drive system. They replaced the ISC.
I don't believe there are any inherently bad engines in early Foretravel diesels if they have been maintained. There have been a few stories about some later models but not to the extent of being a "problem" engine I don't think.
Maintenance records are everything