Jouni,
The Ruhla is not a Deckel copy, more nearly a Thiel copy and it was Thiel from which Deckel were also inspired & developed. Have a look here:
http://www.lathes.co.uk/thiel/index.html
Regarding the table, you have not said whether the alignment is out in a horizontal or vertical plane, or whether it is a fixed table or swivelling one. How much is the error? If the error is small, say a 004″ (0.1mm) over the length and the table is not an adjustable/tilting/swivelling type, you probably need to remove it and check for damage or swarf under or behind the mounting face.
The table is bolted to the front of the vertical face of the ‘carriage’ of the machine. There should be at least 4 bolts in tee slots to retain the table. If you remove the nuts the table can be lifted away. Be careful, the fixed table is probably 40kg.
If it is a tilting &/or swivelling one, it will be a heavier, but you can obviously adjust it after loosening the adjustment locking bolts.
Richard