Do make sure that the engine is under a certain age and hourage. I'm not sure what the exact figure is although I think it's less than 7 years old and under 1500 hrs.
This is only the case if you actuall want to transfer it onto the G reg.
Please don't take these figures as gospel but I was nearly caught out by this whole saga when I nearly bought a nice German registered Cherokee 235 last year. It was about 25% cheaper than its UK counterparts and in beautiful condition.
The payment nearly went through and I fortunately took some advice just beforehand and suddenly pulled up and gave up on it as a bad idea.
A good contact for finding out about German reg a/c is the company who advertise in Flyer mag. I think its called Small World Aviation or something and the guy who runs it is very helpful.
Hope I haven't put you off, just recounting my experiences.
Edited to say:
Oh and another thing is make sure it hasn't had any kind of modification whilst it has been abroad. If it has this will most probably have to be corrected before the CAA will accept it. When I say "modification" I mean even the tinyest thing gets them all excited so do your homework.
If I ever bought abroad I would probably just keep it on its home registration and jump through the hoops each year to keep it airworthy from an engineer abroad.