RE: Too much oil.
You're lucky then... around here (where you can no longer get Castrol M), castor costs the same as synth about $17-$20 a litre!
If you use a traditional synthetic or synth/castor blend such as [link=http://www.the436modelshop.co.nz/item_detail.asp?id=1022&category=122]Klotz SuperTechniplate[/link] at 20% then each litre of fuel contains about $3.33 worth of oil.
Now I usually burn at least 2-3 litres of fuel a weekend (say $10 worth of oil) which means my annual oil-bill (at 20%) is around $500 when using a low-tech oil at old-fashioned ratios.
Now if I use a hi-tech oil like Cooper's Plus C, I can get better protection and performance with just 12% oil. Surprisingly, I end up paying about the same price for Coopers as I do for Klotz, Morgan's or straight castor so...
Do the numbers again and you find that a litre of fuel with 12% oil has only $2 worth of oil. That's $6 a weekend or $300 a year.
The savings over a year amounts therefore to an astonishing $200 more than enough to buy a brand spanking new engine every year.
Now since my oldest engine (a TT46Pro) has been thriving on a diet of 12% for almost two years now and shows no sign of wearing out, I think I'll have banked at least $600 in oil savings before I have to even think about replacing it.
So running 20% or 25% oil is (from my perspective) something like flushing your money down the toilet.