Mimi, please let us know if the bearings are sealed or not. If they are sealed, they will eventually go bad and the bearing cartridge will need to be replaced. But a cartridge should be good for at least several years. If they are not sealed, ie. you have servicable bearings, then they need to be repacked at least annually with new grease. Servicable bearings also need to be adjusted so that the cones, bearings, and cups fit together with the optimal clearance - too tight and the bearings don't roll freely, too loose and the rim can wobble side to side causing poor performance and hub wear. Riding on a loose hub would also permit more water entry and contamination and allow the grease to be washed out. So perhaps your front cones were loose and your rear ones properly adjusted. If you do have servicable hubs on this bike and neither have been serviced in over a year, you might want to ask the mechanic to repack both hubs just because. When he said the rear one was OK, did he mean is was as smooth as if it has just been repacked and adjusted, or not binding and not loose and not horribly gritty? Different mechanics could have different standards here, and different standards for their own bike vs someone else's. Or he could want to save you money and only do them if they are really bad vs giving you optimal performance and maximum hub life.
If you really care about your bike, you should be making the decision on when to service your bearings and keeping track of their condition. You should be feeling your hubs periodically - once a month would be about right to see that they are in proper adjustment and adequately greased. When you get your bike back, Mimi, you can assume that your hubs are well greased and adjusted. So get used to what they feel like at that point and monitor for changes in the future. Here are some ways to check out your hubs:
1) with the wheel on the bike, grab the rim and try to move it side-to-side relative to the frame. Do this at 2 or 3 places along the rim. Any movement at all means the cones are too loose and should be adjusted before you ride the bike again.
2) hold the wheel off the ground and give it a spin. It should spin for quite a long time before slowing down very much. This is somewhat subjective, but if you do this often you should notice a difference when the grease gets old or contaminated or washed out.
3) take the wheel off the bike and turn the axle/cone between your thumb and index finger. It should feel very smooth and non-binding. If it feels gritty or doesn't turn freely or has a "washed out" feeling, it needs service.
4) you can also hear your bearings by putting your ear against the rim and turning the axle (don't know if this works with fancy fiber spokes, but steel spokes will transmit sound and vibration to the rim). Try it if you like, but not sure if this is something you can teach someone over the internet.
Oil is good, grease is better.
2007 Peter Mooney w/S&S couplers/Terry Butterfly
1993 Bridgestone MB-3/Avocet O2 Air 40W
1980 Columbus Frame with 1970 Campy parts
1954 Raleigh 3-speed/Brooks B72