Lots of white/grey smoke after turbo change & Low oil pressure?

[Haywes]

So my old T25G decided it didn't want oil seals anymore, so I bought another one to fit up. I know buying a secondhand turbo is always a gamble, and if it turns out this one is faulty, my original one will be going to Turbo Technics, but I wanted to check before I fork out -even more- money! I did search for this a few times but couldn't find these exact symptoms.

So after getting it all built up and back in, lines connected etc, I primed the turbo, made sure oil pressure was good and then started the car. It ran ok, but slowly the oil pressure dropped, somewhere in the range of 0.5-1bar less than it usually had (which is usually around 2 bar). I made sure everything was tight, couldn't see any issues, but the drain line had a very very very tiny drip of oil now and then, but it was as tight as I could get it, and had a brand new gasket, so not sure on that one either - but would that cause much drop in pressure? it still had between 1.2-1.5bar, but it worried me.

Not long after I discovered the oil pressure had dropped, it started to smoke out of the back lightly. I thought it might have been residue and water/coolant that may have run into the downpipe when I removed the turbo lines before. After it had been running for a while, light revs started to make it puff out a lot of white/greyish (from what I could tell, it was a bit dark by this point) smoke. It seemed to mostly do it once revved lightly a few times. Took it for a quick gentle drive around the block, still smoked a lot, so I put it back on the drive and turned it off. I put my hand over the exhaust when a friend revved it lightly, and I got some water on my hand, but there was a little oil residue inside the pipe too.

Is it possible that the water jacket in the turbo has cracked, and it's letting it into the exhaust? It seems to be more constant supply than residue etc. A lot more. Also, the car didn't smoke like this at all before I changed the turbo, so I have no reason to suspect headgasket etc - car hasn't been run, and the temp gauge was well within normal range. Only thing it did before the turbo change was smoke bluey/grey on overrun, and the old turbo was very oil inside.

Any other ideas what might be causing the issues? Like I said, to avoid any more problems etc, if most of you believe it's just the turbo that's toast, then I'll send my old one off for a proper rebuild and change the oil etc to be safe.

Feedback is appreciated!

[Haywes]

Any input/ideas from anyone?