The only known overhaul manual for the DS-25/2 transaxle was published by ZF in Germany (English & German versions)in about'72 and reprinted by Hall, POCA and god-knows-who-all. Copies are available from all the vendors and some Chapters, with a few fuzzy photos (the original was rotogravure-printed and doesn't copy well). There's another manual that covers the DS-25/1 (Mangusta) and parts of the DS-25/zero (GT-40) transaxles. But even with the manual in hand, some sections are unclear, so be warned. The section on checking ring & pinion drag etc is clear, though. All genuine spares come only from RBT Transmissions in L.A. They bought total rights to this trans back in the late '80s. They may also have original manuals.