Some Lexus GS300 owners report experiencing excessive oil consumption, which necessitates more frequent oil top-offs between standard oil changes. This issue may stem from carbon gumming up the piston rings, leading to oil blow-by and potential engine problems. Lexus has acknowledged such carbon-related issues in models like the IS250 and the 2006 GS300, and they have taken steps to address these by rebuilding affected engines. Additionally, some owners note that maintenance lights are often triggered by oil degradation due to carbon buildup and dirt, which is distinct from the oil consumption problem. While transmission solenoid failures and hard shifting are not explicitly mentioned in the reports, these transmission issues may be linked to maintenance practices and the overall condition of the vehicle. Owners experiencing these transmission problems are advised to consult with a qualified mechanic or Lexus dealership for proper diagnosis and resolution.