there were no genuine MT firmware for 335d and i know the pal who did a bunch of the swaps to 335d mt and later he redone all this cars to 335d with AT, because 335d MT firmware require instant gear switching with doulbe clutch press usage and it is not possible for the average human, only for some very health people
)
so the cheapest way to keep the TS car is to search for the M57D2 3.0d MT swap.
there were 325D LCI cars with M57D2 so the ECU adaptation and coding will not be so complex.