Canon EOS Camera shutter problems
The Canon EOS (Electro Optical System) cameras, are in general very relaible and easy to use. However, after a few years they develop one particular problem: GSS (Greasy Shutter Syndrome!) This describes the problem, how to identify it, and what to do about it.
This is characterised by a black sticky deposit appearing on the shutter blades at the left of the shutter. This sticky grease can cause problems with the proper operation of the shutter.
Apart from the obvious evidence of the black deposit, this can affect the exposure.
It mainly affects the opening shutter, and can retard the shutter leading to uneven exposure with the lower part of the negative (upper part of the print!) receiving less exposure, and often not a smooth gradation, but in steps. This is not too apparent at lower shutter speeds, but at high speeds it can be quite marked. If left unattended, it can even stop the shutter completely!
The cause of the problem
Inside the camera, there is a small synthetic rubber bumper. The material it is made from deteriorates into a soft gooey mess after several years, and it is this which is the source of the nasty black 'grease', which gets on your shutter.
The bumper is intended to soften the landing of the shutter blades as they come to rest after opening. However, if this bumper is removed it actually has no affect on the operation of the shutter.
(In the very long term it might have an effect on some of the shutter pivot points, but that's many years in the future, and the bumper is not any use already. In any case, shutter lifetimes, in terms of the number of operations are huge, usually many hundreds of thousands of operations. If you can afford that much film, then you aren't going to worry about the price of a new camera!)
You could try cleaning the shutter blades with the shutter in place, but there are two problems with that. First, you risk damaging the shutter, second you have'nt removed the source of the problem, and it returns a few days later.
Obviously you don't want to repeatedly clean the shutter, as you multiply the risk of damage each time you do it. Also, to get the goo off you really need to use isoproply alcohol, and you don't want to risk getting any solvent on the focusing screen, or into the AF sensor!
The best solution is to remove the old bumper.
You can do this two ways, the first way is to fish around with a bent wire in the gap at the bottom of the shutter trying to hoick the offending lump out. This is obviously a scary operation, and will usually put more goo on the shutter which will need cleaning! (Some 'repairers' will do this as a quick cheap repair, but you will still and up paying around £30!)
The safer way is a bit time consuming if you aren't familiar with taking these apart, but someone who does it a lot can get it down to less than an hour.
Basically it involves stripping the camera to the point where the shutter itself can be partially dis-assembled, removing the bumper, and the blade assembly. The blades can then be safely cleaned and the shutter re-assembled. (The blades may show a bit of staining afterwards from the solvent, but that's nothing to worry about!)
You can see a shutter being cleaned in an EOS 750 on the mypentax (!) website, (accessible via my 'about me' page on my listings, or my eBay shop: Alchemic Photography as well as a better picture of the problem.)
EOS on eBay
Most of the EOS camera sold on eBay will not have been treated to remove this part. Some of them will not have aged enough for the problem to delevlop, (It will, usually sooner than later!) but most older ones will have this problem.
Some however will have been treated, and it is always advisable to ask if it is not mentioned in the listing. (I always treat the ones I sell!) Be aware of course that the average eBay price, is for an item in average condition, so if the seller replies that it has got a bit of grease, and the problem has not been properly rectified, than that means that you can expect to pay the average price. If it has been cleaned, and the bumper removed, and the seller is willing to guarantee this, then expect to pay more. Remember the minimum you would pay a repairman to get this done would be about £30. (And postage both ways if you have to send it away!) That's if you can find a repairman that would do it. So an extra £30 or so to obtain one with this already done is very likely to be worth it.