I have two marble sized lumps in my scalp, been there for yrs causes no pain or discomfort, are they sebacious cysts?

Pilar cysts. Pilar cysts are common, occurring in 5-10% of the population.[1] greater than 90% occur on the scalp, where pilar cysts are the most common cutaneous cyst. Pilar cysts are the second most frequent type of cyst on the head and neck.[2, 3] pilar cysts are almost always benign, malignant transformation being extremely rare. Pilar cysts may be sporadic or may be autosomal dominantly inherited.
Yes, scalp cyst. Because the scalp is thick-skin, the cysts there are often smaller and firmer than found elsewhere in the body. They do tend to enlarge overtime, albeit slowly. Often, no pain. They don't go away either. People are often annoyed having those bumps there which can get caught during grooming etc...Otherwise, they don't cause medical problems. Consult your doc if you want them removed.. Good luck..