I am rebuilding a 3cylinder a.152. The rebuild kit contained stem seals for the valve assembly, however, when fitting them 2 of them disintegrated when compressing the springs to fit the collets. The factory manual shows that seals are in the assembly, but in the Massey Ferguson version of the same engine the manual shows them missing. Is it necessary to fit these as the head of the valve guide is higher than the oil drain holes in the head and I guess I will only be able to obtain similar seals which are obviously of a poor quality.