I thought you was being sarcastic as there have been numerous threads on this. This is a severe case and being on diesel engines may be why you may not have paid too much attention to it.
Catch it early and it's not too bad. At this stage, the best the OP can do it remove as much of the deposits as possible to save labour costs, unless he is doing it himself
Yes - can be sorted with new seals.
Really? It will only get worse and bear in mind when the engine gets hot it becomes hot and tar-like so it could 'unseal' itself or just build up until it looks like the OP
The earlier you catch it, the easier it is to do. My advice would be get it done
