Not that I'm saying you're wrong, but I'm finding a lot of data like this on the web that contradicts that statement - this comes from a guy that works for AMSOIL:
------------- Synthetic motor oils damage seals.
Untrue. It would be foolhardy for lubricant manufacturers to build a product that is incompatible with seals. The composition of seals presents problems that both petroleum oils and synthetics must overcome. Made from elastomers, seals are inherently difficult to standardize.
Ultimately it is the additive mix in oil that counts. Additives to control seal swell, shrinkage and hardening are required, whether it be a synthetic or petroleum product that is being produced.
( source: http://www.whatprice...thetic-oil.html
That said, some people on other forums HAVE reported that an oil like Castrol High Mileage formula seemed to stop leaking, however they were not sure if it was because it was petroleum-based instead of synthetic, or because olls like the High Mileage have additives meant to recondition the seals...
You represent a motorsports organization so you obviously know Minis - what is your judgement based on? What oil would you recommend for a daily-driver type, non-modded 1275? Do you think an immediate oil change is called for, since I added abut 1/2 a quart of synthetic, or should I resume topping off with Castrol High Mileage and then replace the oil with a petroleum-based product on my next change?
I'll still replace the oil seal when the kit arrives, but I'd like to keep it from springing any fresh leaks afterwards, if I can. I know, I know.. "it's a British car", so leaks are inevitable, but...
Edited by ImagoX, 16 July 2007 - 06:29 PM.