Originally Posted by Machka
... Now, however, I suspect I'll have to replace the chainring, cassette, and chain. Still, I guess getting 35,000 kms out of them isn't too bad. I think what bothers me about having to replace them is that it is only 3 years!! ...
It is possible that you don't need to replace your rings (though given the condition of your chain, this is a long shot). If you use the same ring 90% of the time, it's very likely that you only need to replace one.
Be sure to replace the pulleys on the derailleur. I can't imagine that yours are not toast. It is not necessary to replace the entire derailleur. You can visually check it. My guess is that they will be very obviously and visibly worn.
Originally Posted by Machka
...Somehow I guess I thought everything should last much longer than that....
Think of it like this -- when you ride in slop, grime in the road will get on the chain. You're basically applying grinding paste to the whole system. That it lasted as long as it did is a miracle.
Originally Posted by Machka
...I've got to have several other bits and pieces checked and replaced too ... the bearings in the rear wheel, for example, are shot, and the bottom bracket is very noisy, and my pedals are falling apart ....
Fortunately, none of these things is particularly complicated or expensive if you do it yourself. This is a great opportunity to learn how to take these things apart. After you've messed with your old parts a bit and figure out how they work, you'll feel confident installing the new ones.
One thing to be aware of if you ride in a lot of slop is to check the wear on your rims. Grime on your brakes can just chew up the rims and if they get too thin, that can be a safety issue. I just had to dump a set of wheels earlier this year because I'd worn them out.