Updated October 2008:
'Gold Seal' engines are factory replacement complete engines painted gold instead of the usual maroon or black. They are remanufactured engines i.e. ones that have been exchanged under warranty or for some other reason. They will have been completely dismantled and every component tested and measured to make sure they meet spec, and any that don't are replaced. As such it is probably better than an original engine, which are simply assembled from parts out of a box with the quality and 'correctness' of those parts assumed. I don't know whether replacement parts in a Gold Seal engine were similarly tested, but even if they weren't at least the original parts have been! My roadster came to me with a Gold Seal engine of the correct type for its year, so either it was replaced under warranty or a PO had been very particular about fitting the correct replacement. There were also Silver Seal short engines, i.e. without heads or ancillaries. Gold Seal engines have special prefixes which can be decoded to the original prefixes, see below:
| Engine Type | Compression | Gearbox | Gold Seal Prefix |
| 18G | High | Manual | 48G 279; later 48G 343 |
| 18G | Low | Manual | 48G 280 |
| 18GA | High | Manual | 48G 343 |
| 18GA | Low | Manual | 48G 344 |
| 18GB | High | Manual | 48G 392; later 48G528 48G 739 |
| 18GB | Low | Manual | 48G 393 |
| 18GD/GG | Low | Manual | 48G 527; later 48G 736 |
| 18GD/GG | High | Manual | 48G 528; later 48G 702 48G 755 |
| 18GD/GG | Low | Auto | 48G 529; later 48G 736 |
| 18GD/GG | High | Auto | 48G 530; later 48G 755 |
| 18GF/GH | High | Manual | 48G 539; later 48G 704 |
| 18GJ/GK | High | Manual | 48G 704 |
| 18V581/582/583 | High | Manual/Auto | 48G 733 |
| 18V779/780 | High | Manual | 48G 733 |
| 18V581/582/583 | Low | Manual/Auto | 48G 736 |
| 18V584/585 | Low | Manual | 48G 737 |
| 18V672/673 | Low | Manual | 48G 737 |
| 18V836/837 | Low | Manual | BHM 1074 |
| 18V797/798 | Low | Manual | BHM 1105 |
| 18V801/802 | Low | Manual | BHM 1105 |
| 18V846/847 | High | Manual | BHM 1111 |
Note 2 Added February 2010: In practice Gold Seal engines have an 'E' or 'N' suffix letter as in 48G733E nnnnnn. The 'E' refers to an exchange engine, either fitted by a dealer or an owner. 'N' refers to an outright purchase i.e. no return of a faulty unit.