Now look what followed me home today ...
Nice, I've got one too (followed me home in a similar way as yours). Service manual with schematics can be found on the net. It has a nice sharp trace, but one thing I really dislike: All the settings are lost on power down, the scope always starts to the same defaults (no battery inside to replace that could backup the settings). And if the LCD backlight is burned out (it's incandescent), the LCD is hard to read.
Oh, wait a moment - mine has more buttons, indeed it's a PM3055. Looks quite similar otherwise.
I know that behaviour of settings memory loss over powercycle from my PM3065, too.
I came across a little extension that plugs in to a 9 pin SUB-D port on the back of the unit that looks like a RS232-connector (in fact I don't know if it is one).
This extension contains a RAM buffered by a rechargeable battery.
With this hooked on, the oscilloscope remembers its last settings and restores them after powering on.
In fact it looses memory again if I don't use the oscilloscope over a longer period of time. Haven't researched that really so I can't give you a number of days.
I got it from a local surplus dealer, Helmut Singer but I'm nearly confident he doesn't sell them any more because the company closed and is currently in liquidation (sells rests of their stock though).
If you are interested I'll crawl behind my PM 3065 and have a look if I can find out it's name or number -perhaps I can take a look into it.