Sorry to hear, I'm assuming you have a burnt valve from the 0 compression

.
Maybe it's just stuck if you're lucky, I recommend using some proper synthetic in it.
Were you driving just fine before the RP and what weight and brand were you using? RP is known to burn and thin out especially on a lot of Subaru's so the consumption issue may be partially a fault of the oil. I also believe RP is not truly synthetic unless you got their racing line.
If Royal Purple street products are not 100% synthetic, why are they priced similar to a full synthetic?
[INDENT] The Synerlec technology provides the best protection and performance increases available, however, it is very expensive. We have blended our street oils to exceed the performance characteristics of any other blended or "Full" synthetic. If having a full synthetic is important, we have our racing line which can be considered a "Full" synthetic.
[/INDENT]