I had the exact same problem on my last 90, I didn't know the size either so just bought an assorted pack of e clips off ebay for a couple of quid which did the job.
This is what I bought.
E CLIPS CIRCLIP SNAP RING CLIP 28 pc ASSORTMENT | eBay
Thanks Arron.
A cheap fix but a few hours work getting the turbo off to get to it.
I changed the injection pump last weekend and it went like a rocket for two days, then this happened.
hmm, i might be wrong, but i think you can get to it with your fingers.. bit faffy though
you should be able to close the wastegate to get it closer.
tried pliers? or if you connect an airline to the actuator at 15psi it will make it move down and you should be able to get it on... maybe
might be worth a try before taking all off
Turbo now working as it should.
I couldn't get to it without taking the whole thing off but it's done.
Get a new manifold gasket before you start.
How do you know what length the actuator arm should be? I've just bought a used turbo and I now have a black smoke issue.