According to President Erdoğan Germans are blocking machinery (probably related to propulsion) for Turkish frigates, turbines for the Akkuyu nuclear plant, and the Eurofighter deal.
Germans are also slowing down the Reis class submarine project.
They did block MTU engines and STM & DzKK agreed to switch with MAN engines. Renk cross connect gears are, however, delivered or ordered with no further issues. This is strange, to my opinion the gearbox is much more crucial since it is custom made and would cause delays in the project since there is no alternative supplier.
MTU either tells 'there is no engine in stock' and postpones the delivery to two to three years later, while it is known that they have a stock, or they tell that there issues with the customs, regulations and export regulations.
Anyone who is slightly familiar with German bureucracy would understand these much better, if they don't desire to sell a nut, they would find a regulation as an alibi.