We purchased a 2005 Forest River Lexington 5 years ago while living in Washington which makes it about the same age as the one you are looking at. There are a lot of positives about the Lex. However, there are some negatives; they included water leakage at the rubber seals around the slides. Be careful and check at the bottom of the slides for signs of water damage. There was also leakage at the joint where the cabover joined the chassis. I found water in the fiberglass canopy only after removing the entertainment system and looking into the cabover. Since you probably don't have a overhead bed in the Lex, any leaks will be difficult to spot. One way to check is to inspect the cabover from the outside and look to see if the cabover has pulled away from the chassis and exposed a crack in the seal. I sealed the crack and used a sponge to remove the pool of water. I also drilled a small hole in the cabover so any future water leaks will be drained out.
Also, inspect the awnings very carefully. Being in western Canada, there is a chance that the awning may have become mildewed and rotten in the past 9 years. If so, negotiate that in your offer. For some reason the Lex seems to use the cheapest awnings made. I replaced mine with awnings made by a manufacturer in Vancouver WA...not Vancouver BC.
Like any other RV made, you will encounter mechanical issues along the way. I had the fuel pump replaced; a slide motor replaced, grey water valve replaced, etc. This can happen to ANY motorhome so don't blame Forest River. You might want to log onto the Forest River Lexington website for more information pertinent to this particular RV before you buy. Whatever you decide, good luck.