ive an m90 and was told capacitors on these generally dont leak due to the quality  of workmen-ship of manifactor "like victor company" these are made in japan i had my m90 in for deck repaired and the tech said everything was ok with the radio and it is over thirty yrs old... this is my expierance

Thought;  Make a recording of how well it sounds Now before you replace any capacitors, Then Replace the capacitors in the power supply and in the amplifer section best as you would know, then replay your first recording  using the same music as before you replaced the 'caps' then you will know the difference of, and the worthiness of doing such maintenance

The electrolytic ones - Would the the "Only" One's to replace as they are the most susceptible to going bad  

Me Neither  

To add to this, the ones in the power supply are most heavily stressed, so if you don't want to replace them all, just change the large value capacitors near the power input.

I would add though, if its working fine then probably best leave it alone, the quality of 70-80's Japanese made stuff is very good.