Guess you are talking about XRS040N100 and XRS050N200? **broken link removed**
The potting compound is most likely two component silicone elastomer, made e.g. by Dow Corning and available from electronics catalog distributors. Alternatively polyurethane elastomer, harder and less easy to cut.
Maybe someone has a schematic, but I don't expect VMI to publish it because switch mode power supplies are rarely intended for third party repair, potted devices even less.
In some cases it might be possible though, e.g. if simple components like filter capacitors or HV rectifiers are defective.