Answer
"Seamaster 128" is not an Omega catalog name. Sellers use the term for two things: the Omega Seamaster 120 dive watch, and watches with case reference numbers that contain the digits 128. No factory document exists under the name Seamaster 128. Treat the label as marketing, not as proof of a model.
Check the movement first
A Seamaster 120 from the 1960s and 1970s carries calibre 565, 552, 562, or 601. The rotor is signed. The bridges carry the Omega symbol and the calibre number. Count the jewels. A 17-jewel automatic under a dial that should hold 24 jewels is a swap. Serial numbers sit on the bridge and should fall inside the year range in published Omega serial tables.
Case and caseback
Original casebacks show a hippocampus medallion stamped in relief. The reference number is stamped on the inside of the caseback. Stamps on fakes are shallow, uneven, or use a modern font. Case edges on refinished metal look soft, and lugs get polished thin. Measure the case. A Seamaster 120 dive case runs about 36 to 37 mm across without the crown. A 42 mm case with a Seamaster dial is a different watch.
Dial and hands
Redials are the most common problem. Read the "Seamaster" text under the Omega logo. Letters on a redial are thick, uneven, or spaced wrong. Lume plots should sit in a neat ring and age to one tone. Mixed plot colors point to a re-lume. Hands should match the dial: sword hands on the early 120, with lume the same shade as the dial plots. Date wheels came in several languages. A wheel in a language Omega did not ship with that reference is a swap.
Frankenwatches
Many listings combine a genuine movement, an aftermarket case, and a printed dial. Each part can be real and the watch still wrong. Ask for a photo of the movement outside the case, the inside of the caseback, and the serial numbers on both. Numbers from different production years are a mismatch.
Papers and records
Omega issues an Extract of the Archives. The document lists the case number and movement number on file, which confirms the factory shipped that pair. It does not confirm that the dial, hands, bezel, or crown on the watch are original. Expect a fee and a wait of several weeks.
Before you buy
- Ask for movement, caseback, and dial photos in daylight.
- Compare the reference number with Omega tables, not with the seller's text.
- Check serial numbers against the year of the reference.
- Have a watchmaker open the case. Five minutes of inspection costs less than a return shipment.
- Price is a signal. A complete, correct 1960s dive Seamaster often reaches four figures in US dollars. A listing at a tenth of that number is not a bargain.