well first of all, check that it isnt leaking any more oil, and that it isnt burning it either (keep an eye on the level)

Then it could be worth cleaning the egr valve if it has one (haynes manual). Over time they get full of carbon and just gum up. If its been driven by a biddy at no more than 2k rpm all its life then it will be clogged to fook. Just keep ranting it