Another thread revival but one of the few where I might be able to add some value.
I too have had a Wahl professional for 25 years bought through a barber friend, which I have always cut my hair with since. Prevents helmet hair on the motorbike and saves a fair amount of money in the process.
Last year it got a bit noisy and wasn't cutting so well so I took it to a barber supply place in Perth and asked about options. They said it needed sharpening, which wasn't that much cheaper than a new set of blades so I was skeptical of the value. But they also said that new blades aren't that sharp and I will be blown away once they are actually sharpened properly.
So I gave them a go at sharpening and I was blown away by the result. Now the thing is almost silent, so smooooth and mows down hair like it's not there at all. I was very impressed - it's now much better than it was when it was new!
BTW I also got read the riot act for not using enough oil on it - I just used four or five drops after each cut but apparently that is nowhere near enough. It really needs a good soak of oil in every orifice until it is operating almost silent again. Start and stop to re-oil a couple of times as well. So don't skimp on the oil!
Anyway, I learnt a few things out of that process and thought I should share them.
Another vote for the Wahl Pro's, I have been using them on my head with no comb attached for probably around 6 -7 years now and they have never missed a beat. A few weeks ago I removed the blades and gave them a sharpen on one of my oil stones and then a little hone on the old leather strap and they are just buzzing away like they were on the very first day I bought them. As @RazorPlay said always keep the oil up to the blades and they will last a very very long time.