1999 Corolla crankcase deposits

Just acquired vehicle with 119,000 miles. Previous owner had good paper trail of vehicle maintenance. Owner states he used Castrol synthetic oil. I did some basic maintenance right away...plugs, PCV, belt, etc. Although the old plugs were in good shape, they were not spec plugs (i.e. single ground vs. double ground). Noticed some black deposits inside valve cover baffle (inside oil fill port). PCV valve was also gunked up and I replaced it. Checked oil level and noticed some small specs of gritty deposits (carbon) on the dipstick. Used some Seafoam(r) thru intake manifold and also in crankcase to help lift these deposits. Getting ready to change the oil. Other than continuing to work with slowly removing these deposits, does anyone have any recommendations what to keep an eye on? How to prevent reoccurance? Potential problems that may arise as a result. I'm thinking the restriction in the PCV may have led to the deposits...similar to the Sienna "sludge" issue.