If you ride often, replacing the 16ml/cc's of splash bath oil in each leg of the lowers should be done every 3 - 4 months, more often if ridden when wet and muddy. Sounds like it is time to service the lowers. You can use car engine oil. About 10-30 multi-grade and synthetic is better.
It's easy to do. The service manual can be downloaded and gives step by step instructions. Probably some u-tube videos around too if you search.
It's easy to do. The service manual can be downloaded and gives step by step instructions. Probably some u-tube videos around too if you search.