All jobs are DIY if . . .
you have a lift!!! My tech is kind enough to let me use one of his lifts so it takes the sting out.
The charcoal filter is one of those jobs but it doesn't need a lift! My car had about 98K when I changed it, about 1 year ago. The filter wasn't that bad but was very dirty.
The pre-filter (also charcoal) located on top of the blower is one that should changed. It's also a little pricey also but is a key filter. Thiss one is easy to get to; 15 min job.
Never have replaced or seen a cat replaced on these cars. I would think that it should last 150K+ miles. This is based on what I see replaced at my tech's shop.
Regards . . . . JimF
'94 S500 Cpe
Visit my Mercedes Web Page